Other Comprehensive Income (Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Other comprehensive income (loss), after tax and net of reclassifications into Net income		$ 2,460	$ (10,581)	$ (2,361)
Debt securities
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Net unrealized gains (losses)		840	(10,866)	(2,445)
Less: Net realized gains (losses) reclassified to earnings		(913)	(723)	6
Other comprehensive income (loss), before tax and net of reclassifications into Net income		1,753	(10,143)	(2,451)
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Net unrealized gains (losses)		(202)	2,561	576
Less: Net realized gains (losses) reclassified to earnings		217	171	(2)
Income tax benefit (expense) related to items of other comprehensive income		(419)	2,390	578
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Net unrealized gains (losses)		638	(8,305)	(1,869)
Less: Net realized gains (losses) reclassified to earnings		(696)	(552)	4
Other comprehensive income (loss), after tax and net of reclassifications into Net income		1,334	(7,753)	(1,873)
Cash flow hedge derivatives
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Net unrealized gains (losses)		(237)	(3,536)	(632)
Less: Net realized gains (losses) reclassified to earnings		(1,540)	(260)	494
Other comprehensive income (loss), before tax and net of reclassifications into Net income		1,303	(3,276)	(1,126)
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Net unrealized gains (losses)		65	833	149
Less: Net realized gains (losses) reclassified to earnings		376	61	(117)
Income tax benefit (expense) related to items of other comprehensive income		(311)	772	266
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Net unrealized gains (losses)		(172)	(2,703)	(483)
Less: Net realized gains (losses) reclassified to earnings		(1,164)	(199)	377
Other comprehensive income (loss), after tax and net of reclassifications into Net income		992	(2,504)	(860)
Pension and other postretirement benefit plan adjustments
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		166	(363)	486
Other comprehensive income (loss), before tax and net of reclassifications into Net income		166	(363)	486
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		(40)	85	(114)
Income tax benefit (expense) related to items of other comprehensive income		(40)	85	(114)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		126	(278)	372
Other comprehensive income (loss), after tax and net of reclassifications into Net income		126	(278)	372
Other
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		5	(5)	4
Other comprehensive income (loss), before tax and net of reclassifications into Net income		5	(5)	4
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		3	(41)	(4)
Income tax benefit (expense) related to items of other comprehensive income		3	(41)	(4)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Less: Net realized gains (losses) reclassified to earnings		8	(46)
Other comprehensive income (loss), after tax and net of reclassifications into Net income		8	(46)
Continuing Operations
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Other comprehensive income (loss), before tax and net of reclassifications into Net income		3,227	(13,787)	(3,087)
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Income tax benefit (expense) related to items of other comprehensive income		(767)	3,206	726
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, After Reclassification Adjustments, after Tax [Abstract]
Other comprehensive income (loss), after tax and net of reclassifications into Net income		$ 2,460	$ (10,581)	$ (2,361)