Subsequent Event - Additional Information (Detail) (USD $)	9 Months Ended		0 Months Ended		0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Oct. 29, 2014 Subsequent events Variable Interest Entity, Primary Beneficiary Automobile Loan Securitizations	Oct. 29, 2014 Subsequent events Variable Interest Entity, Primary Beneficiary Automobile Loan Securitizations	Oct. 23, 2014 Subsequent events March 2014 Repurchase Program
Subsequent Event [Line Items]
Total shares repurchased					8,337,875
Shares acquired for treasury	$ 474,000,000	$ 664,000,000			$ 180,000,000
Redemption date			Oct. 29, 2014		Oct. 23, 2014
Other Long Term Debt				$ 1,000,000,000