Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 62	$ 60	$ 64	$ 57
Provision (credit) for losses on lending-related commitments	2	(2)	0	1
Balance at end of period	$ 64	$ 58	$ 64	$ 58