Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 64	$ 57	$ 55
Provision (credit) for losses on lending-related commitments	4		2
Balance at end of period	68	64	57
Previously Reported [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 63	57
Provision (credit) for losses on lending-related commitments		6
Balance at end of period		$ 63	$ 57