Equity-Based Compensation Information Related to Stock Options (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of stock options
Pretax expense for stock options	$ 5	$ 11	$ 28
After-tax expense for stock options	4	8	19
Proceeds from stock options exercised	71	157	27
Income tax benefit related to stock options exercised
Tax benefit classified in operating activities in the Consolidated Statements of Cash Flows	13	0	2
Excess tax benefit classified in financing activities in the Consolidated Statements of Cash Flows	33	0	4
Intrinsic value of stock options exercised	62	98	19
Total fair value of stock options vesting	5	11	22
Stock options exercised, shares	2,541	6,096	1,688
Non-vested stock option compensation expense not yet recognized	$ 9
Non-vested stock options weighted average period for total compensation expense to be recognized	2.2