Earnings Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Line Items]
Net income (loss)	$ 640	$ (39)	$ 1,941	$ 805
Weighted-average shares outstanding	340,207,037	338,385,734	339,523,388	338,139,477
Share-based compensation plans	2,665,676	0	2,831,798	2,733,434
Adjusted weighted-average shares outstanding and assumed conversions	342,872,713	338,385,734	342,355,186	340,872,911
Basic earnings per share (US$ per share)	$ 1.88	$ (0.11)	$ 5.71	$ 2.38
Diluted earnings per share (US$ per share)	$ 1.86	$ (0.11)	$ 5.67	$ 2.36
Anti-dilutive share conversions	1,449,610	2,295,260	1,193,839	223,987