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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Non-cash compensation expense and capitalized non-cash compensation
Nonvested restricted stock and restricted stock units (RSUs)	3,000,000		3,000,000
OSOs outstanding	2,000,000		2,000,000
Non-cash compensation expense and capitalized non-cash compensation	$ 16	$ 48	$ 26	$ 85
Outperform Stock Options
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	2	11	4	16
Restricted Stock Units and Shares
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	6	14	12	21
Performance Restricted Stock Units [Member]
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	3	0	3	0
401(k) Match Expense
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	5	5	12	13
Restricted Stock Unit Bonus Grant
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	0	14	(5)	29
Management Incentive and Retention Plan
Non-cash compensation expense and capitalized non-cash compensation
Stock-based compensation expense	$ 0	$ 4	$ 0	$ 6
Non-qualified stock options
Non-cash compensation expense and capitalized non-cash compensation
OSOs outstanding	9,000		9,000