Loans Held for Sale - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		$ 1,809		$ 1,809	$ 2,185
Transfer of loans to held for sale, net				1,588	1,850	$ 316
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		844		844	2,095
Valuation allowance		55		55	21
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		965		965	90
Valuation allowance		57		57	13
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		725		725	151
Global Banking - Loans Transferred to Held for Sale [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		102		102	49
Global Banking [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		827		827	200
Commercial Real Estate [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial real estate loans sold during the period				1,161
Loss on sale of real estate loans held for sale				3
Loans transferred to held for investment				612
Total loans held for sale		17		17	1,895
Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		890		890	11
Unpaid principal balance of loans transferred to held-for-sale	[1]			568
Transfer of loans to held for sale, net	[1]			473
Residential Mortgage And Home Equity Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance of loans transferred to held-for-sale	[1]		$ 648
Transfer of loans to held for sale, net	[1]		628
Subprime [Member] | Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		3		3	3
Other Income [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of amortized cost or fair value adjustment attributed to non-credit factors				45
Additional lower of amortized cost or fair value adjustment		$ 4		8
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				$ 35	$ 16	$ 5
Provision for Credit Losses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower of cost or fair value adjustment attributed to credit factors			$ 11

[1] The decrease in past due loans at December 31, 2016 reflects the impact of transfers of certain residential mortgage loans to held for sale during 2016. See Note 7, "Loans Held for Sale" for additional details.