Statement Of Financial Position [Abstract]

SANTANDER UK PLC - Filing #1571969

Concept	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2021-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2020-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2019-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31	As at 2018-12-31
Statement of financial position [abstract]
Assets [abstract]
Non-current assets [abstract]
Property, plant and equipment	—	—	1,548,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	1,734,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Investments in subsidiaries, joint ventures and associates reported in separate financial statements	—	—	201,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	172,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Assets	—	—	287,098,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	292,332,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Equity and liabilities [abstract]
Equity [abstract]
Issued capital	—	—	3,105,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	3,105,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Retained earnings	—	—	5,053,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	4,348,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Share premium	—	—	5,620,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	5,620,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Other equity interest	—	—	2,191,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	2,191,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Other reserves	—	—	133,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	510,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Equity attributable to owners of parent	—	—	16,102,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	15,774,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Non-controlling interests	—	—	— GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	162,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Equity	5,053,000,000 GBP	2,191,000,000 GBP	16,102,000,000 GBP	107,000,000 GBP	25,000,000 GBP	16,102,000,000 GBP	5,620,000,000 GBP	— GBP	1,000,000 GBP	3,105,000,000 GBP	4,348,000,000 GBP	162,000,000 GBP	481,000,000 GBP	15,774,000,000 GBP	3,105,000,000 GBP	2,191,000,000 GBP	1,000,000 GBP	5,620,000,000 GBP	15,936,000,000 GBP	28,000,000 GBP	15,857,000,000 GBP	2,191,000,000 GBP	160,000,000 GBP	1,000,000 GBP	16,017,000,000 GBP	5,620,000,000 GBP	4,546,000,000 GBP	23,000,000 GBP	371,000,000 GBP	3,105,000,000 GBP	5,000,000 GBP	5,620,000,000 GBP	15,758,000,000 GBP	151,000,000 GBP	15,909,000,000 GBP	1,991,000,000 GBP	23,000,000 GBP	256,000,000 GBP	3,119,000,000 GBP	4,744,000,000 GBP
Liabilities [abstract]
Liabilities	—	—	270,996,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	276,396,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—
Equity and liabilities	—	—	287,098,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	292,332,000,000 GBP	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—