Long-Term Debt - Additional Information (Detail) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Mar. 31, 2013 Beginning Amount	Mar. 31, 2013 Ending Amount	Sep. 30, 2013 Parent company Senior Debt Obligations Fixed Rate 1.45 Percent Notes Due 2018	Mar. 31, 2013 Parent company Senior Debt Obligations Fixed Rate 1.45 Percent Notes Due 2018	Sep. 30, 2013 Parent company Senior Debt Obligations Fixed Rate .90 Percent Notes Due 2016	Mar. 31, 2013 Parent company Senior Debt Obligations Fixed Rate .90 Percent Notes Due 2016	Sep. 30, 2013 Parent company Senior Debt Obligations Floating Rate Notes Due 2016 Three Month LIBOR	Mar. 31, 2013 Parent company Senior Debt Obligations Floating Rate Notes Due 2016 Three Month LIBOR	Sep. 30, 2013 Parent company Variable Interest Entity, Primary Beneficiary Automobile Loan
Debt Instrument
Global Bank Note Program			$ 20,000,000,000	$ 25,000,000,000
Issue of senior notes to third party investors		1,300,000,000				600,000,000		400,000,000		300,000,000
Other Long Term Debt											$ 1,200,000,000
Debt Instrument, Interest Rate Terms	3-month LIBOR plus 41 basis points
Maturity date(s) Start					Feb. 28, 2013		Feb. 28, 2013		Feb. 28, 2013
Maturity date(s) End					Feb. 28, 2018		Feb. 26, 2016		Feb. 26, 2016