Fair Values - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Assets at fair value
Loans	$ 3,178		$ 3,178		$ 3,687
Other assets—Other investments	26		26		114
Other assets—Premises, equipment and software	0		0		0
Total	3,204		3,204		3,801
Liabilities at fair value
Other liabilities and accrued expenses—Lending commitments	(225)		(225)		357
Total	(225)		(225)		357
Assets
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(34)	$ (10)	(28)	$ (21)
Loans
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(27)	(5)	(12)	1
Other assets—Other investments
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(3)	(2)	(8)	(9)
Other assets—Premises, equipment and software
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(4)	(3)	(8)	(13)
Liabilities
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(19)	31	82	41
Other liabilities and accrued expenses—Lending commitments2
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(19)	$ 31	82	$ 41
Level 2
Assets at fair value
Loans	1,513		1,513		2,307
Other assets—Other investments	0		0		14
Other assets—Premises, equipment and software	0		0		0
Total	1,513		1,513		2,321
Liabilities at fair value
Other liabilities and accrued expenses—Lending commitments	(161)		(161)		292
Total	(161)		(161)		292
Level 3
Assets at fair value
Loans	1,665		1,665		1,380
Other assets—Other investments	26		26		100
Other assets—Premises, equipment and software	0		0		0
Total	1,691		1,691		1,480
Liabilities at fair value
Other liabilities and accrued expenses—Lending commitments	(64)		(64)		65
Total	$ (64)		$ (64)		$ 65