Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 15, 2016	Jun. 30, 2015
Bank Servicing Fees		$ 46	$ 49	$ 148	$ 164
Principal Amount Outstanding of Loans Serviced	[1]	30,200		30,200			$ 27,700
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		285,397		285,397			278,197
Mortgage Servicing Rights, Fair Value [Member]
Bank Servicing Fees		100	94	301	272
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		165,300		165,300			160,200
Principal Amount Outstanding of Loans Serviced For Third Parties		135,400		135,400			129,600
Unpaid Principal Balance of Outstanding Underlying MSRs Purchased				0	10,900
Principal Amount Sold on Loans Serviced for Third Parties				350	464
Servicing Asset at Fair Value, Amount		1,628	1,119	1,628	1,119	$ 1,307	1,572
Asset-backed Securities, Securitized Loans and Receivables [Member]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	[1]	138,774		138,774			131,914
indirect auto loan servicing rights [Member]
Servicing Asset at Amortized Cost		2		2			4
Bank Servicing Fees			2		5
Servicing Asset									$ 13
Commercial Mortgage Servicing Rights [Member]
Servicing Asset at Amortized Cost		61		61			62
Bank Servicing Fees		6	0	17	0
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		5,300		5,300			4,800
Servicing Asset at Fair Value, Amount		69		69			62
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets								$ 62
Consumer Portfolio Segment [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	[1]	337		337			512
Proceeds from Securitizations of Consumer Loans						$ 1,000
Pillar Financial [Member]
Bank Servicing Fees		3	$ 0	11	$ 0
Principal Amount Outstanding of Loans Serviced For Third Parties		$ 24,900		$ 24,900			$ 22,900

[1] Excludes loans that have completed the foreclosure or short sale process (i.e., involuntary prepayments).