Recent Accounting Pronouncements (Details) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2010	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011
Recent Accounting Pronouncements
Cumulative effect decrease in retained earnings				$ 1,400,000,000
Cumulative effect increase in assets	5,500,000,000
Cumulative effect increase in liabilities	5,100,000,000
Cumulative effect increase in appropriated retained earnings	473,000,000	473,000,000
Cumulative effect increase to retained earnings due to adoption of new accounting principle, net			$ 132,000,000