Other Comprehensive Income (Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Increase in net unrealized gains (losses) on securities, pre-tax	$ (2,445)	$ 2,113	$ 1,529
Less: Net realized gains (losses) reclassified to earnings, pre-tax	6	302	40
Net increase (decrease), pre-tax	(2,451)	1,811	1,489
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Increase in net unrealized gains (losses) on securities, tax effect	576	(485)	(351)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(2)	(69)	(9)
Effect of income taxes	578	(416)	(342)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Increase in net unrealized gains (losses) on securities, after tax	(1,869)	1,628	1,178
Less: Net realized gains (losses) reclassified to earnings, after tax	4	233	31
Net increase (decrease), after-tax	(1,873)	1,395	1,147
Net unrealized gains (losses) on cash flow hedge derivatives [Abstract]
Increase in net unrealized gains (losses) on cash flow hedges, pre-tax	(632)	918	334
Less: Net realized gains (losses) reclassified to earnings, pre-tax	494	421	37
Net increase (decrease), pre-tax	(1,126)	497	297
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax [Abstract]
Increase in net unrealized gains (losses) on cash flow hedges, tax effect	149	(211)	(77)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(117)	(97)	(9)
Effect of income taxes	266	(114)	(68)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Increase in net unrealized gains (losses) on cash flow hedges, after tax	(483)	707	257
Less: Net realized gains (losses) reclassified to earnings, after tax	377	324	28
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	(860)	383	229
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, pre-tax	486	82	158
Net increase (decrease), pre-tax	486	82	158
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, tax effect	(114)	(19)	(36)
Net increase (decrease), tax	(114)	(19)	(36)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Net pension and other postretirement benefit plan activity and other reclassified to earnings, after-tax	372	63	122
Net increase (decrease), after-tax	372	63	122
Other Comprehensive Income Other Adjustments [Abstract]
Net unrealized gains (losses) on other transactions, pre-tax	4	10	17
Total Other, net activity, Before tax	4	10	17
Net unrealized gains (losses) on other transactions, tax effect	(4)	5	5
Effect of income taxes	(4)	5	5
Net unrealized gains (losses) on other transactions, after tax		15	22
Total Other, net activity, After tax		15	22
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(3,087)	2,548	1,966
Income tax benefit (expense) related to items of other comprehensive income	726	(577)	(442)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(2,361)	1,971	1,524
Continuing Operations
Other Comprehensive Income Other Adjustments [Abstract]
Net unrealized gains (losses) on other transactions, pre-tax	4	10	17
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(3,087)	2,400	1,961
Income tax benefit (expense) related to items of other comprehensive income	726	(544)	(441)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(2,361)	1,856	1,520
Discontinued Operations
Other Comprehensive Income Other Adjustments [Abstract]
Other comprehensive income (loss), before tax and net of reclassifications into Net income		148	5
Income tax benefit (expense) related to items of other comprehensive income		(33)	(1)
Other comprehensive income (loss), after tax and net of reclassifications into Net income		$ 115	$ 4