Shareholders' Equity (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		86 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Shareholders' equity activity [Roll Forward]
Balance at beginning of period	$ 15,790,000,000	$ 13,216,000,000
Transactions with shareholders	73,000,000	94,000,000
Comprehensive income (loss)	(10,000,000)	637,000,000
Payments of dividends to shareholders	(116,000,000)	(83,000,000)
Balance at end of period	15,737,000,000	13,864,000,000	15,737,000,000
Stock Repurchased During Period, Shares	1		97
Payments for Repurchase of Common Stock	50,000,000		3,319,000,000
Treasury Stock Acquired, Average Cost Per Share	$ 40.70
Stock Repurchase Program, Authorized Amount	5,000,000,000
Common Stock, Dividends, Per Share, Declared	$ 0.125
Dividend Per Share Declared Increases	$ 0.035
Company shareholders' equity
Shareholders' equity activity [Roll Forward]
Balance at beginning of period	15,765,000,000	13,198,000,000
Transactions with shareholders	74,000,000	95,000,000
Comprehensive income (loss)	(13,000,000)	634,000,000
Payments of dividends to shareholders	(116,000,000)	(83,000,000)
Balance at end of period	15,710,000,000	13,844,000,000	15,710,000,000
Noncontrolling interest in consolidated subsidiaries
Shareholders' equity activity [Roll Forward]
Balance at beginning of period	25,000,000	18,000,000
Transactions with shareholders	(1,000,000)	(1,000,000)
Comprehensive income (loss)	3,000,000	3,000,000
Payments of dividends to shareholders	0	0
Balance at end of period	$ 27,000,000	$ 20,000,000	$ 27,000,000