Loans Held for Sale - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Mar. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		$ 765				$ 765		$ 1,809
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		620				620		844
Valuation allowance		56				56		55
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		145				145		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		389				389		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		231				231		102
Residential Mortgage [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale		78				78		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		24				495
Loans held for sale, sold, at aggregate carrying value		22				467
Gain (loss) on sale of loans held for sale		1				44
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		(2)			$ 4	(1)	$ 30
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					5		38
Additional lower of amortized cost or fair value adjustment			$ (5)		$ 6		$ 6
Other Income [Member] | Residential Mortgage And Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional lower of amortized cost or fair value adjustment		(3)				(2)
HSBC Finance Corporation [Member] | Residential Mortgage And Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of residential mortgage loans		$ 71				$ 71		$ 558