Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income
Beginning Balance	$ 878	$ 3,995	$ 5,394	$ 88
Other net changes	1,530	1,616	(2,986)	5,523
Ending Balance	2,408	5,611	2,408	5,611
Net unrealized gain (loss), excluding transfers to available for sale from held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes	1,532	1,615	(2,976)	4,465
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)
Other [Member]
Accumulated Other Comprehensive Income
Other net changes		$ 1		$ 1