Loans Held for Sale - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		$ 507			$ 507		$ 1,809
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		431			431		844
Valuation allowance		8			8		55
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		76			76		965
Valuation allowance		7			7		57
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		375			375		725
Commercial Loans - Transferred to Held for Sale [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		49			49		102
Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		12			12		890
Transfer of loans to held for sale, unpaid principal balance							568
Transfer of loans to held for sale, at aggregate carrying value							473
Loans held for sale, sold, unpaid principal balance	$ 364
Loans held for sale, sold, at aggregate carrying value	276
Gain (loss) on sale of loans held for sale	$ (2)
Residential Mortgage And Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of loans to held for sale, unpaid principal balance				$ 648
Transfer of loans to held for sale, at aggregate carrying value				628
Loans held for sale, sold, unpaid principal balance		84			579
Loans held for sale, sold, at aggregate carrying value		68			535
Gain (loss) on sale of loans held for sale		6			50
Subprime [Member] | Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		2			2		$ 3
Other Income [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of amortized cost or fair value adjustment attributed to non-credit factors		$ 4		7	5	$ 37
Other Income [Member] | Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of amortized cost or fair value adjustment attributed to non-credit factors				4		42
Additional lower of amortized cost or fair value adjustment			$ (5)	2		$ 8
Other Income [Member] | Residential Mortgage And Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional lower of amortized cost or fair value adjustment					$ (2)
Provision for Credit Losses [Member] | Residential Mortgage And Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of cost or fair value adjustment attributed to credit factors				$ 11