Employee Benefit Benefits and Stock-Based Compensation - Non-cash compensation expensed and capitalized (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation expense
Stock- based compensation expense	$ 74	$ 152	$ 136
Capitalized Noncash Compensation	(1)	(1)	(1)
Non-cash compensation expense	73us-gaap_ShareBasedCompensation	151us-gaap_ShareBasedCompensation	135us-gaap_ShareBasedCompensation
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost	4	5	9
Outperform Stock Options
Stock-based compensation expense
Stock- based compensation expense	8	21	14
Restricted Stock Units and Shares
Stock-based compensation expense
Stock- based compensation expense	34	38	40
401(k) Match Expense
Stock-based compensation expense
Stock- based compensation expense	23	24	23
Restricted Stock Unit Bonus Grant
Stock-based compensation expense
Stock- based compensation expense	(5)	59	46
Management Incentive and Retention Plan
Stock-based compensation expense
Stock- based compensation expense	$ 0	$ 10	$ 13

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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-Publisher FASB

-Name Accounting Standards Codification

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

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- Definition

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

+ References

No definition available.

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