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
	Mar. 31, 2013	Mar. 31, 2012
Non-cash compensation expense and capitalized non-cash compensation
Nonvested restricted stock and restricted stock units (RSUs)	4,000,000
OSOs outstanding	2,000,000
Stock-based compensation expense	$ 37	$ 24
Capitalized Non-cash Compensation	0	0
Non-cash compensation expense and capitalized non-cash compensation	37	24
Outperform Stock Options
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	5	2
Restricted Stock Units and Shares
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	7	4
401(k) Match Expense
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	8	7
Restricted Stock Unit Bonus Grant
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	15	11
Management Incentive and Retention Plan
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	$ 2	$ 0
Non-qualified stock options
Non-cash compensation expense and capitalized non-cash compensation
OSOs outstanding	59,000