Total Equity and Other Comprehensive Income (Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax [Abstract]
Increase in net unrealized gains (losses) on securities, pre-tax	$ 42	$ 221	$ 2,283	$ 1,583
Less: Net realized gains (losses) reclassified to earnings	32	7	255	27
Net increase (decrease), pre-tax	10	214	2,028	1,556
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax [Abstract]
Increase in net unrealized gains (losses) on securities, tax effect	(9)	(51)	(525)	(363)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(7)	(2)	(59)	(6)
Effect of income taxes	(2)	(49)	(466)	(357)
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	33	170	1,758	1,220
Less: Net realized gains (losses) reclassified to earnings, after tax	25	5	196	21
Net increase (decrease), after-tax	8	165	1,562	1,199
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax [Abstract]
Increase in net unrealized gains (losses) on cash flow hedges, pre-tax	15	84	960	438
Less: Net realized gains (losses) reclassified to earnings, pre-tax	134	5	282	5
Net increase (decrease), pre-tax	(119)	79	678	433
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	(3)	(19)	(221)	(100)
Less: Net realized gains (losses) reclassified to earnings, tax effect	(30)	(1)	(65)	(1)
Effect of income taxes	27	(18)	(156)	(99)
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	12	65	739	338
Less: Net realized gains (losses) reclassified to earnings, after tax	104	4	217	4
Net increase (decrease), after-tax	(92)	61	522	334
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	2	2	(3)	63
Net increase (decrease), pre-tax	2	2	(3)	63
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			1	(14)
Effect of income taxes			1	(14)
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	2	2	(2)	49
Net increase (decrease), after-tax	2	2	(2)	49
Other Comprehensive Income Other Adjustments [Abstract]
Net unrealized gains (losses) on other transactions, pre-tax	0	4	10	14
Net increase (decrease), pre-tax	0	4	10	14
Net unrealized gains (losses) on other transactions, tax effect	10	(7)	(9)	(11)
Effect of income taxes	10	(7)	(9)	(11)
Net unrealized gains (losses) on other transactions, after tax	10	(3)	1	3
Net increase (decrease), after-tax	10	(3)	1	3
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(107)	276	2,861	2,037
Total other comprehensive income (loss), tax effect	35	(70)	(663)	(475)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	(72)	206	2,198	1,562
Continuing Operations
Other Comprehensive Income Other Adjustments [Abstract]
Other comprehensive income (loss), before tax and net of reclassifications into Net income	(107)	299	2,713	2,066
Total other comprehensive income (loss), tax effect	35	(74)	(630)	(481)
Other comprehensive income (loss), after tax and net of reclassifications into Net income	$ (72)	225	2,083	1,585
Discontinued Operations
Other Comprehensive Income Other Adjustments [Abstract]
Other comprehensive income (loss), before tax and net of reclassifications into Net income		(23)	148	(29)
Total other comprehensive income (loss), tax effect		4	(33)	6
Other comprehensive income (loss), after tax and net of reclassifications into Net income		$ (19)	$ 115	$ (23)