Earnings Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share [Abstract]
Net income (loss)	$ 765	$ 640	$ 328	$ 973	$ 735	$ (39)	$ 594	$ 250	$ 2,706	$ 1,540	$ 3,085
Weighted-average shares outstanding									339,843,438	338,159,409	339,685,143
Share-based compensation plans									2,903,512	2,620,815	1,561,244
Adjusted weighted-average shares outstanding and assumed conversions									342,746,950	340,780,224	341,246,387
Basic earnings per share (US$ per share)	$ 2.24	$ 1.88	$ 0.96	$ 2.87	$ 2.17	$ (0.11)	$ 1.75	$ 0.74	$ 7.96	$ 4.55	$ 9.08
Diluted earnings per share (US$ per share)	$ 2.22	$ 1.86	$ 0.96	$ 2.84	$ 2.15	$ (0.11)	$ 1.74	$ 0.73	$ 7.89	$ 4.52	$ 9.04
Potential anti-dilutive share conversions									896,591	111,326	256,868