Summary of Significant Accounting Policies - Narrative (Details)		1 Months Ended	12 Months Ended
	Jan. 02, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment payments	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jan. 03, 2015	Oct. 31, 2014 USD ($)
Summary of Significant Accounting Policies [Line Items]
Typical repayment period			30 days
Probable loss experience period			10 years
Allowance for credit losses		$ 31,000,000	$ 54,000,000	$ 31,000,000
Number of delinquent payments that can be moved | payments			2
Additional operating segments | segment			2
Number of operating segments | segment			2
Intercompany subvention receivable		384,000,000	$ 573,000,000	384,000,000
Intercompany Receivable - Commercial Lending		176,000,000	229,000,000	176,000,000
Intercompany Receivables - Wholesale financing		289,000,000		289,000,000
Intercompany Receivable - Commercial Receivables		433,000,000	362,000,000	433,000,000
Related party taxes payable		636,000,000	$ 0	636,000,000
Earnings asset leverage ratio			8.3
Ownership percentage by noncontrolling owners (percent)	10.00%
Contributions from GM		700,000,000
Total borrowing capacity			$ 5,200,000,000
New Accounting Pronouncement, Early Adoption, Effect [Member] | Other Assets [Member]
Summary of Significant Accounting Policies [Line Items]
Issuance costs		116,000,000		116,000,000
Parent Company [Member]
Summary of Significant Accounting Policies [Line Items]
Subvention income			3,600,000,000	1,200,000,000	$ 451,000,000
Amortization of lease subvention			$ 1,000,000,000	311,000,000	$ 159,000,000
Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life (in years)			1 year
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Estimated useful life (in years)			30 years
Earnings asset leverage ratio			9.5
Consumer Finance Receivables [Member]
Summary of Significant Accounting Policies [Line Items]
Contractually delinquent period			120 days
Commercial Finance Receivables [Member]
Summary of Significant Accounting Policies [Line Items]
Typical repayment period			90 days
Contractually delinquent period			360 days
Commercial Finance Receivables [Member] | Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Credit facility expiration period			6 months
Commercial Finance Receivables [Member] | Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Payment period after loan is called			60 days
Credit facility expiration period			18 months
Corporate Revolving Credit Facility [Member] | Line of Credit [Member]
Summary of Significant Accounting Policies [Line Items]
Total borrowing capacity							$ 4,000,000,000.0
Junior Subordinated Revolving Credit Facility [Member] | Line of Credit [Member]
Summary of Significant Accounting Policies [Line Items]
Total borrowing capacity							$ 1,000,000,000.0
Secured Debt [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] | Long-term Debt [Member]
Summary of Significant Accounting Policies [Line Items]
Issuance costs		41,000,000		41,000,000
Unsecured Debt [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] | Long-term Debt [Member]
Summary of Significant Accounting Policies [Line Items]
Issuance costs		75,000,000		75,000,000
Tax Year 2010 and 2011 [Member]
Summary of Significant Accounting Policies [Line Items]
Related party taxes payable		$ 296,000,000		$ 296,000,000
Tax Year 2014 [Member]
Summary of Significant Accounting Policies [Line Items]
Contributions from GM			$ 649,000,000
Subsidiaries [Member]
Summary of Significant Accounting Policies [Line Items]
Ownership percentage	40.00%
Ownership percentage by noncontrolling owners (percent)	5.00%
SAIC-GMAC [Member]
Summary of Significant Accounting Policies [Line Items]
Ownership percentage						35.00%
Aggregate consideration	$ 1,000,000,000
Proceeds from sale of interest	$ 125,000,000