Stock-Based Compensation - Non-cash compensation expense and capitalized non-cash compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Non-cash compensation expense and capitalized non-cash compensation
Nonvested restricted stock and restricted stock units (RSUs)	4,000,000		4,000,000
OSOs outstanding	2,000,000		2,000,000
Stock-based compensation expense	$ 48	$ 29	$ 85	$ 53
Capitalized Non-cash Compensation	0	0	0	0
Non-cash compensation expense and capitalized non-cash compensation	48	29	85	53
Outperform Stock Options
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	11	4	16	6
Restricted Stock Units and Shares
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	14	14	21	18
401(k) Match Expense
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	5	6	13	13
Restricted Stock Unit Bonus Grant
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	14	5	29	16
Management Incentive and Retention Plan
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	$ 4	$ 0	$ 6	$ 0
Non-qualified stock options
Non-cash compensation expense and capitalized non-cash compensation
OSOs outstanding	55,000		55,000