Securities - Fair Value of Investments with Continuous Unrealized Loss Position (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale:
Less than 12 months, Fair value	$ 23,073,000,000	$ 23,012,000,000
Less than 12 months, Unrealized losses	440,000,000	92,000,000
12 months or more, Fair value	8,998,000,000	10,774,000,000
12 months or more, Unrealized losses	236,000,000	146,000,000
Total, Fair value	32,071,000,000	33,786,000,000
Total, Unrealized losses	676,000,000	238,000,000
AOCI, transfers from AFS to HTM Securities, gross unrealized losses, greater than 12 months	59,000,000	65,000,000
AOCI, transfers from AFS to HTM Securities, gross unrealized losses, less than 12 months	0	0
Grantor Trust
Available-for-sale:
Less than 12 months, Fair value	3,900,000,000
Agency RMBS
Available-for-sale:
Less than 12 months, Fair value	5,200,000,000	8,373,000,000
Less than 12 months, Unrealized losses	53,000,000	33,000,000
12 months or more, Fair value	6,969,000,000	5,912,000,000
12 months or more, Unrealized losses	166,000,000	110,000,000
Total, Fair value	12,169,000,000	14,285,000,000
Total, Unrealized losses	219,000,000	143,000,000
U.S. Treasury
Available-for-sale:
Less than 12 months, Fair value		1,976,000,000
Less than 12 months, Unrealized losses		16,000,000
12 months or more, Fair value		766,000,000
12 months or more, Unrealized losses		4,000,000
Total, Fair value		2,742,000,000
Total, Unrealized losses		20,000,000
Sovereign debt/sovereign guaranteed
Available-for-sale:
Less than 12 months, Fair value	2,801,000,000	4,045,000,000
Less than 12 months, Unrealized losses	9,000,000	10,000,000
12 months or more, Fair value	104,000,000	225,000,000
12 months or more, Unrealized losses	0	1,000,000
Total, Fair value	2,905,000,000	4,270,000,000
Total, Unrealized losses	9,000,000	11,000,000
Agency commercial mortgage-backed securities (“MBS”)
Available-for-sale:
Less than 12 months, Fair value	1,440,000,000	1,960,000,000
Less than 12 months, Unrealized losses	14,000,000	12,000,000
12 months or more, Fair value	522,000,000	775,000,000
12 months or more, Unrealized losses	6,000,000	5,000,000
Total, Fair value	1,962,000,000	2,735,000,000
Total, Unrealized losses	20,000,000	17,000,000
Foreign covered bonds
Available-for-sale:
Less than 12 months, Fair value	2,934,000,000	1,009,000,000
Less than 12 months, Unrealized losses	33,000,000	4,000,000
12 months or more, Fair value	255,000,000	690,000,000
12 months or more, Unrealized losses	3,000,000	3,000,000
Total, Fair value	3,189,000,000	1,699,000,000
Total, Unrealized losses	36,000,000	7,000,000
Collateralized loan obligations (“CLOs”)
Available-for-sale:
Less than 12 months, Fair value	3,456,000,000	1,066,000,000
Less than 12 months, Unrealized losses	189,000,000	2,000,000
12 months or more, Fair value	554,000,000	1,499,000,000
12 months or more, Unrealized losses	41,000,000	14,000,000
Total, Fair value	4,010,000,000	2,565,000,000
Total, Unrealized losses	230,000,000	16,000,000
Commercial paper/certificates of deposit (“CDs”)
Available-for-sale:
Less than 12 months, Fair value	1,225,000,000
Less than 12 months, Unrealized losses	2,000,000
12 months or more, Fair value	0
12 months or more, Unrealized losses	0
Total, Fair value	1,225,000,000
Total, Unrealized losses	2,000,000
Supranational
Available-for-sale:
Less than 12 months, Fair value	1,663,000,000	1,336,000,000
Less than 12 months, Unrealized losses	6,000,000	6,000,000
12 months or more, Fair value	203,000,000	360,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	1,866,000,000	1,696,000,000
Total, Unrealized losses	6,000,000	6,000,000
Foreign government agencies
Available-for-sale:
Less than 12 months, Fair value	942,000,000	1,706,000,000
Less than 12 months, Unrealized losses	3,000,000	2,000,000
12 months or more, Fair value	50,000,000	47,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	992,000,000	1,753,000,000
Total, Unrealized losses	3,000,000	2,000,000
Non-agency commercial MBS
Available-for-sale:
Less than 12 months, Fair value	1,050,000,000	525,000,000
Less than 12 months, Unrealized losses	60,000,000	2,000,000
12 months or more, Fair value	37,000,000	45,000,000
12 months or more, Unrealized losses	3,000,000	0
Total, Fair value	1,087,000,000	570,000,000
Total, Unrealized losses	63,000,000	2,000,000
Other ABS
Available-for-sale:
Less than 12 months, Fair value	1,283,000,000	456,000,000
Less than 12 months, Unrealized losses	38,000,000	3,000,000
12 months or more, Fair value	193,000,000	305,000,000
12 months or more, Unrealized losses	5,000,000	2,000,000
Total, Fair value	1,476,000,000	761,000,000
Total, Unrealized losses	43,000,000	5,000,000
U.S. government agencies
Available-for-sale:
Less than 12 months, Fair value	73,000,000	377,000,000
Less than 12 months, Unrealized losses	2,000,000	2,000,000
12 months or more, Fair value	0	0
12 months or more, Unrealized losses	0	0
Total, Fair value	73,000,000	377,000,000
Total, Unrealized losses	2,000,000	2,000,000
Non-agency RMBS
Available-for-sale:
Less than 12 months, Fair value	737,000,000	101,000,000
Less than 12 months, Unrealized losses	27,000,000	0
12 months or more, Fair value	96,000,000	113,000,000
12 months or more, Unrealized losses	12,000,000	7,000,000
Total, Fair value	833,000,000	214,000,000
Total, Unrealized losses	39,000,000	7,000,000
Non-agency RMBS | Grantor Trust
Available-for-sale:
Less than 12 months, Fair value	97,000,000	2,000,000
Less than 12 months, Unrealized losses	7,000,000	1,000,000
12 months or more, Fair value	1,000,000	2,000,000
12 months or more, Unrealized losses	1,000,000	1,000,000
State and political subdivisions
Available-for-sale:
Less than 12 months, Fair value	37,000,000	0
Less than 12 months, Unrealized losses	2,000,000	0
12 months or more, Fair value	15,000,000	16,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	52,000,000	16,000,000
Total, Unrealized losses	2,000,000	0
Corporate bonds
Available-for-sale:
Less than 12 months, Fair value	232,000,000	82,000,000
Less than 12 months, Unrealized losses	2,000,000	0
12 months or more, Fair value	0	21,000,000
12 months or more, Unrealized losses	0	0
Total, Fair value	232,000,000	103,000,000
Total, Unrealized losses	$ 2,000,000	$ 0