Debt Obligations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended									1 Months Ended															0 Months Ended					1 Months Ended					3 Months Ended			3 Months Ended			3 Months Ended											12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Aug. 31, 2011	Mar. 31, 2013 Fiscal Quarter Ending Before December 31 2013 [Member]	Mar. 31, 2013 Fiscal Quarter Ending on or After December 31, 2013, and Prior to December 31, 2014 [Member]	Mar. 31, 2013 Each Fiscal Quarter Ending December 31, 2014 and Beyond [Member]	Mar. 31, 2013 Fiscal Quarters Ending Prior to December 31, 2013 [Member]	Mar. 31, 2013 Fiscal Quarters Ending On Or After December 31, 2013 [Member]	Aug. 31, 2011 Secured Debt [Member]	Mar. 31, 2013 Term Loan [Member]	Dec. 31, 2011 Term Loan [Member]	Aug. 22, 2012 Incremental Facility Agreement [Member]	Mar. 31, 2013 Revolving [Member]	Dec. 31, 2011 Revolving [Member]	Mar. 31, 2013 5% Notes Due 2022 [Member]	Sep. 17, 2012 5% Notes Due 2022 [Member]	Dec. 31, 2011 5% Notes Due 2022 [Member]	Mar. 31, 2013 4.625% Notes Due 2021 [Member] [Member]	Dec. 18, 2012 4.625% Notes Due 2021 [Member] [Member]	Dec. 31, 2011 4.625% Notes Due 2021 [Member] [Member]	Mar. 31, 2013 Other [Member]	Dec. 31, 2011 Other [Member]	Aug. 22, 2012 Incremental Facility Agreement [Member] Secured Debt [Member]	Aug. 23, 2012 Incremental Facility Agreement [Member] Term Loan [Member]	Mar. 31, 2013 Incremental Facility Agreement [Member] Term Loan [Member]	Aug. 22, 2012 Incremental Facility Agreement [Member] Term Loan [Member]	Aug. 22, 2012 Incremental Facility Agreement [Member] Revolving [Member]	Mar. 31, 2013 Line of Credit [Member]	Sep. 30, 2011 Secured Debt [Member] Term Loan [Member]	Mar. 31, 2013 Secured Debt [Member] Term Loan [Member]	Aug. 31, 2011 Secured Debt [Member] Term Loan [Member]	Aug. 31, 2011 Secured Debt [Member] Revolving [Member]	Mar. 31, 2013 Base Rate [Member] Secured Debt [Member]	Mar. 31, 2013 Base Rate [Member] Minimum [Member] Secured Debt [Member]	Mar. 31, 2013 Base Rate [Member] Maximum [Member] Secured Debt [Member]	Mar. 31, 2013 Federal Funds Rate [Member] Secured Debt [Member]	Mar. 31, 2013 LIBOR [Member] Minimum [Member] Secured Debt [Member]	Mar. 31, 2013 LIBOR [Member] Maximum [Member] Secured Debt [Member]	Mar. 31, 2013 Redemption Period One [Member]	Mar. 31, 2013 Twelve Month Period Commencing On July 15, 2017 [Member] 5% Notes Due 2022 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On July 15, 2017 [Member] Senior Notes due 2022 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On July 15, 2018 [Member] Senior Notes due 2022 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On July 15, 2019 [Member] Senior Notes due 2022 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On July 15, 2020 [Member] Senior Notes due 2022 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On February 15, 2017 [Member] Senior Notes due 2021 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On February 15, 2018 [Member] Senior Notes due 2021 [Member]	Mar. 31, 2013 Twelve Month Period Commencing On February 15, 2019 [Member] Senior Notes due 2021 [Member]	Mar. 31, 2013 Prior To February 15, 2017 [Member] Senior Notes due 2021 [Member]	Mar. 31, 2013 Redemption Period Two [Member]	Mar. 31, 2013 Redemption Period Three [Member]	Dec. 31, 2012 Prior to February 15, 2016 [Member] [Member] Senior Notes due 2022 [Member]	Dec. 31, 2012 Prior to July 15, 2015 [Member] Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 2,091		$ 1,963								$ 832	$ 850		$ 145	$ 0	$ 600	$ 600	$ 600	$ 500	$ 500	$ 500	$ 14	$ 13
Short-term borrowings	77	72
Long-term debt	2,014	1,891
Secured Credit Facility Maximum Borrowing Amount	1,700									1,400																						700	700
Credit Facility, Term										5 years
Additional Amount of Incremental Term Loan or Incremental Revolving Commitment																								300			150	150
Line of Credit Facility, Reduction in Borrowing Capacity From Usage of Letters of Credit																													17
Debt Instrument, Periodic Payment																									3.75					17.50
Debt Instrument, Amont Due at Maturity Date																										97.5					455.0
Debt Instrument, Basis Spread on Variable Rate																																		1.00%			0.50%
Debt Instrument, Margin for Base Rate Loans																																			0.25%	1.50%		1.25%	2.50%
Deferred Finance Costs, Noncurrent, Net				29									3				11			7
Debt Instrument Covenant Consolidated Leverage Ratio					3.50	3.25	3.00																																	3.5										3.25	3.5
Debt Instrument Covenant Interest Coverage Ratio								3.5	4.0
Interest Coverage Ratio Determination Period	four consecutive fiscal quarters
Debt Instrument, Interest Rate, Stated Percentage																	5.00%			4.625%
Percentage of Principle Amount Notes Were Sold At																	100.00%			100.00%
Debt Instrument Redemption Price As Percentage Of Principle Amount																																									100.00%	102.50%	101.667%	100.833%	100.00%	102.313%	101.156%	100.00%	100.00%			104.625%	105.00%
Debt Instrument, Note Redemption, Percentage of Aggregate Principle Amount																																																				35.00%
Debt Instrument, Fair Value Disclosure	$ 2,090		$ 1,970