Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ 624	$ 1,000	$ 2,290	$ 1,676
Other comprehensive income (loss), tax effect	(150)	(231)	(531)	(386)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	21,873	19,844	21,203	16,250
Other comprehensive income, net of tax	474	769	1,759	1,290
Ending Balance	22,335	20,671	22,335	20,671
Net unrealized gains on available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	602	758	1,757	1,319
Other comprehensive income (loss), before reclassifications, tax effect	(146)	(181)	(419)	(312)
Other comprehensive income (loss), before reclassifications, net activity	456	577	1,338	1,007
Reclassification adjustment, pre-tax activity				1
Reclassification adjustment, tax effect				0
Reclassification adjustment, net activity				1
Other comprehensive income (loss), pre-tax activity	602	758	1,757	1,320
Other comprehensive income (loss), tax effect	(146)	(181)	(419)	(312)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,694	204	812	(227)
Other comprehensive income, net of tax	456	577	1,338	1,008
Ending Balance	2,150	781	2,150	781
Net unrealized gains on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	83	240	624	351
Other comprehensive income (loss), before reclassifications, tax effect	(17)	(50)	(131)	(74)
Other comprehensive income (loss), before reclassifications, net activity	66	190	493	277
Reclassification adjustment, pre-tax activity	(62)	1	(94)	3
Reclassification adjustment, tax effect	13	0	20	0
Reclassification adjustment, net activity	(49)	1	(74)	3
Other comprehensive income (loss), pre-tax activity	21	241	530	354
Other comprehensive income (loss), tax effect	(4)	(50)	(111)	(74)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	824	249	422	160
Other comprehensive income, net of tax	17	191	419	280
Ending Balance	841	440	841	440
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, pre-tax activity	1	1	3	2
Reclassification adjustment, tax effect	0	0	(1)	0
Reclassification adjustment, net activity	1	1	2	2
Other comprehensive income (loss), pre-tax activity	1	1	3	2
Other comprehensive income (loss), tax effect	0	0	(1)	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(41)	(44)	(42)	(45)
Other comprehensive income, net of tax	1	1	2	2
Ending Balance	(40)	(43)	(40)	(43)
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	2,477	409	1,192	(112)
Ending Balance	$ 2,951	$ 1,178	$ 2,951	$ 1,178