Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
U.K.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 266	$ 438
Capital loss carryforwards	577	411
Interest carryforwards	121	203
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	49	1
Capital loss carryforwards	112	112
Interest carryforwards	1,220	355
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	378	376
Capital loss carryforwards	123	123
Interest carryforwards	573	172
Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	400	308
Capital loss carryforwards	42	29
Interest carryforwards	$ 34	$ 159