Stock-Based Compensation (Schedule of Unrecognized Compensation Costs and Amortization Periods) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Nonvested Stock Options [Member]
Unrecognized compensation costs	$ 10
Weighted-Average Service Years, amortization period	0.9
Restricted Shares and Time-Vested Restricted Share Units [Member]
Unrecognized compensation costs	7
Weighted-Average Service Years, amortization period	1.1
Nonvested Performance-Based Restricted Share Units [Member]
Unrecognized compensation costs	$ 41
Weighted-Average Service Years, amortization period	1.5

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph h

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration