Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income
Beginning Balance	$ 20,670	$ 56,060	$ 21,745	$ 20,670
Other net changes		(6,503)	5,306	340
Ending Balance		56,261	56,060	21,745
Accumulated other comprehensive income, tax expense (benefit)		(2,033)	1,659	106
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income
Beginning Balance	(252)	5,394	88	(252)
Other net changes		(6,503)	5,306	340
Ending Balance		(1,109)	5,394	88
Net unrealized gain (loss), excluding transfers to available for sale from held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes		(6,492)	4,246	309
Accumulated other comprehensive income, tax expense (benefit)		(2,029)	1,322	96
Net unrealized gain (loss) on securities transferred to available for sale from held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes	$ 19		1,057	19
Accumulated other comprehensive income, tax expense (benefit)			336	6
Other reclassifications included in other revenue [Member]
Accumulated Other Comprehensive Income
Other net changes		(3)	(3)	(5)
Accumulated other comprehensive income, tax expense (benefit)		(1)	(1)	(1)
Amortization of amounts previously recorded upon transfer to held to maturity from available for sale [Member]
Accumulated Other Comprehensive Income
Other net changes				27
Accumulated other comprehensive income, tax expense (benefit)				9
Other [Member]
Accumulated Other Comprehensive Income
Other net changes		(8)	6	(10)
Accumulated other comprehensive income, tax expense (benefit)		$ (3)	$ 2	$ (4)