Summary of Notes Payable (Parenthetical) (Detail) In Millions, unless otherwise specified	Sep. 30, 2012 8.50% senior notes due May 2019	Dec. 31, 2011 8.50% senior notes due May 2019	Sep. 30, 2012 6.45% senior notes due August 2040 USD ($)	Dec. 31, 2011 6.45% senior notes due August 2040 USD ($)	Sep. 30, 2012 6.90% senior notes due December 2039 USD ($)	Dec. 31, 2011 6.90% senior notes due December 2039 USD ($)	Sep. 30, 2012 3.45% senior notes due August 2015	Dec. 31, 2011 3.45% senior notes due August 2015	Sep. 30, 2012 2.65% senior notes due February 2017 USD ($)	Jul. 31, 2012 2.65% senior notes due February 2017 USD ($)	Feb. 29, 2012 2.65% senior notes due February 2017 USD ($)	Sep. 30, 2012 4.00% senior notes due February 2022 USD ($)	Feb. 29, 2012 4.00% senior notes due February 2022 USD ($)	Sep. 30, 2012 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Dec. 31, 2011 2.26% yen-denominated Uridashi notes due September 2016 JPY (¥)	Sep. 30, 2012 1.47% yen-denominated Samurai notes due July 2014 JPY (¥)	Dec. 31, 2011 1.47% yen-denominated Samurai notes due July 2014 JPY (¥)	Dec. 31, 2011 1.87% yen-denominated Samurai notes paid June 2012 JPY (¥)	Sep. 30, 2012 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Dec. 31, 2011 1.84% yen-denominated Samurai notes due July 2016 JPY (¥)	Sep. 30, 2012 Variable interest rate yen-denominated Samurai notes due July 2014 JPY (¥)	Dec. 31, 2011 Variable interest rate yen-denominated Samurai notes due July 2014 JPY (¥)	Sep. 30, 2012 3.60% yen-denominated loan due July 2015 JPY (¥)	Dec. 31, 2011 3.60% yen-denominated loan due July 2015 JPY (¥)	Sep. 30, 2012 3.00% yen-denominated loan due August 2015 JPY (¥)	Dec. 31, 2011 3.00% yen-denominated loan due August 2015 JPY (¥)	Sep. 30, 2012 5.50% subordinated notes due September 2052 USD ($)
Debt Instrument [Line Items]
Notes payable, interest rate	8.50%	8.50%	6.45%	6.45%	6.90%	6.90%	3.45%	3.45%	2.65%	2.65%	2.65%	4.00%	4.00%	2.26%	2.26%	1.47%	1.47%	1.87%	1.84%	1.84%	1.34%	1.34%	3.60%	3.60%	3.00%	3.00%	5.50%
Notes payable, principal amount			$ 450	$ 450	$ 400	$ 400			$ 650	$ 250	$ 400	$ 350	$ 350	¥ 8,000	¥ 8,000	¥ 28,700	¥ 28,700	¥ 26,600	¥ 15,800	¥ 15,800	¥ 5,500	¥ 5,500	¥ 10,000	¥ 10,000	¥ 5,000	¥ 5,000	$ 450
Notes payable, issuance premium									7
Notes payable, underwriting discount			$ 2	$ 2	$ 4	$ 4						$ 1