Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income
Beginning Balance	$ 2,408	$ 5,611	$ 5,394	$ 88
Other net changes	(1,155)	75	(4,141)	5,598
Ending Balance	1,253	5,686	1,253	5,686
Net unrealized gain (loss), excluding transfers to available for sale from held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes	$ (1,155)	77	(4,131)	4,542
Net unrealized gain on securities transferred to available for sale from held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes				1,057
Other reclassifications included in other revenue [Member]
Accumulated Other Comprehensive Income
Other net changes		$ (2)	$ (10)	(2)
Other [Member]
Accumulated Other Comprehensive Income
Other net changes				$ 1