Accumulated Other Comprehensive Income - Change in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	$ 17,159	$ 16,532	$ 17,279	$ 16,367
Other comprehensive income (loss) before reclassifications			(312)	858
Other Comprehensive Income (Loss), Net of Tax	196	228	(326)	828
Amounts reclassified from AOCI			(14)	(30)
Balance, ending	17,590	16,737	17,590	16,737
Adjustments to Additional Paid in Capital, Other	73	40	51	22
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	136	211	203	(115)
Other comprehensive income (loss) before reclassifications	12	40	(35)	352
Amounts reclassified from AOCI	(18)	(6)	(38)	8
Balance, ending	130	245	130	245
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(81)	165	392	(93)
Other comprehensive income (loss) before reclassifications	205	214	(275)	506
Amounts reclassified from AOCI	(19)	(35)	(12)	(69)
Balance, ending	105	344	105	344
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(564)	(638)	(582)	(654)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	18	15	36	31
Balance, ending	(546)	(623)	(546)	(623)
Accumulated Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	0	0	0	0
Other comprehensive income (loss) before reclassifications	(2)	0	(2)	0
Amounts reclassified from AOCI	0	0	0	0
Balance, ending	(2)	0	(2)	0
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning	(509)	(262)	13	(862)
Other comprehensive income (loss) before reclassifications	215	254
Other Comprehensive Income (Loss), Net of Tax	196	228	(326)	828
Amounts reclassified from AOCI	(19)	(26)
Balance, ending	$ (313)	$ (34)	$ (313)	$ (34)