Debt (Narrative) (Details)	3 Months Ended				12 Months Ended			3 Months Ended				12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended					12 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2012 USD ($)	Jun. 30, 2011 USD ($) item	Jun. 30, 2011 CNY item	Sep. 30, 2010 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Mar. 31, 2012 Debentures, 4.75%, Due 2042 [Member] USD ($)	Mar. 31, 2012 Debentures, 4.70%, Due 2037 [Member] USD ($)	Dec. 31, 2012 Debentures, 1.45% percentage, Due 2017 [Member] USD ($)	Dec. 31, 2012 Debentures, 8.875%, Due 2021 [Member] USD ($)	Dec. 31, 2012 Debentures, 8.875%, Due 2021 [Member] USD ($)	Dec. 31, 2012 Debentures, 8.875%, Due 2016 [Member] USD ($)	Dec. 31, 2012 Debentures, 8.875%, Due 2016 [Member] USD ($)	Dec. 31, 2012 Debentures, 6.75%, Due 2013 [Member] USD ($)	Dec. 31, 2012 Debentures, 6.75%, Due 2013 [Member] USD ($)	Dec. 31, 2010 Notes 6.05% [Member] USD ($)	Sep. 30, 2010 Notes 5.75% [Member] USD ($)	Sep. 30, 2010 Notes 4.25% [Member] USD ($)	Sep. 30, 2010 Notes 6.2% [Member] USD ($)	Sep. 30, 2010 Notes 5.9% [Member] USD ($)	Dec. 31, 2010 Notes 6.25% [Member] USD ($)	Dec. 31, 2012 Debentures, 5.90%, Due 2014 [Member] USD ($)	Dec. 31, 2012 Debentures, 6.20%, Due 2016 [Member] USD ($)	Dec. 31, 2010 Amended Credit Facility [Member] USD ($)	Dec. 31, 2012 Debentures, 6.75%, Due 2013 [Member]	Dec. 31, 2012 Debentures, 8.875%, Due 2016 [Member]	Dec. 31, 2012 Debentures, 8.875%, Due 2021 [Member]	Dec. 31, 2012 Medium-Term Notes, Average Rate 7.66%, Due Through 2023 [Member]	Dec. 31, 2012 Debentures, 6.85%, Due 2029 [Member]	Dec. 31, 2012 Debentures, Callable, 7.25%, Due 2036 [Member]
Debt Instrument [Line Items]
Weighted average interest rate					5.30%	2.10%
Fair value of long-term debt					$ 3,700,000,000	$ 2,600,000,000
Line of credit facility, maximum borrowing amount		642,000,000	4,000,000,000																						1,000,000,000
Line of credit facility number of installments		6	6
Line of credit facility final payment due, years from date of first advance		5 years	5 years
Amount borrowed under credit facility					377,000,000	120,000,000
Line of credit facility, expiration date																									Dec. 01, 2015
Repurchase of debt					280,000,000		364,000,000										100,000,000
Redemption of principal																						48,000,000
Par value of issued senior unsecured notes								500,000,000	250,000,000	250,000,000								400,000,000	300,000,000
Interest rate on debt								4.75%	4.70%	1.45%	8.875%	8.875%	8.875%	8.875%	6.75%	6.75%	6.05%	5.75%	4.25%	6.20%	5.90%	6.25%	5.90%	6.20%		6.75%	8.875%	8.875%	7.66%	6.85%	7.25%
Maturity date								Mar. 15, 2042	Mar. 15, 2037	Nov. 15, 2017							Jun. 15, 2015	Aug. 15, 2040	Aug. 15, 2020	Mar. 15, 2016	Mar. 15, 2014	Feb. 18, 2010
Debt maturity date											2021		2016		2013								2014	2016		2013	2016	2021	2023	2029	2036
Proceeds from issuance of long-term debt and capital securities, net	742,000,000									248,000,000								394,000,000	295,000,000
Net carrying amount of senior unsecured note debt				234,000,000													100,000,000
Repurchase of senior unsecured notes											13,000,000	13,000,000	11,000,000	11,000,000	51,000,000	51,000,000				126,000,000	100,000,000		100,000,000	74,000,000
Net loss on early redemption of senior unsecured notes				$ 30,000,000	$ (26,000,000)		$ (30,000,000)								$ 26,000,000