Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 58	$ 48	$ 57	$ 55
Provision (credit) for losses on lending-related commitments	2	9	3	2
Balance at end of period	$ 60	$ 57	$ 60	$ 57

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Balance Type:	na
Period Type:	duration