Common Stock (Details 1) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2011 Y	Sep. 30, 2011 Y	Jun. 30, 2011 Y	Mar. 31, 2011 Y	Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009
Stock options status and activity
Shares Under Option Outstanding Beginning Balance	2,957,407	3,071,457	3,174,753	3,168,474	3,168,474
Weighted Average Exercise Prices, Outstanding, Beginning Balance	$ 16.83	$ 16.51	$ 16.34	$ 14.27	$ 14.27
Weighted Average Remaining Life In Years, Beginning Balance	4.0	4.2	4.4	4.3	4.3
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 54	$ 76	$ 80	$ 68	$ 68
Shares Under Option, Granted	173	1,649	2,711	201,133
Weighted Average Exercise Prices, Granted	$ 24.97	$ 44.02	$ 43.51	$ 45.42
Shares under option expired	(10,000)			(56,046)
Weighted average exercise price expired	$ 1.57			$ 3.66
Shares Under Option, Forfeited	(17,716)	(450)	(23,841)	(13,184)
Weighted Average Exercise Prices, Forfeited	$ 1.82	$ 4.03	$ 14.26	$ 9.36
Shares Under Option, Exercised	(186,665)	(115,249)	(82,166)	(125,624)
Weighted Average Exercise Prices, Exercised	$ 10.19	$ 8.94	$ 11.50	$ 17.10
Aggregate Intrinsic Value, Exercised	3	3	3	3	13	10	4
Shares Under Option Outstanding Ending Balance	2,743,199	2,957,407	3,071,457	3,174,753	2,743,199	3,168,474
Weighted Average Exercise Prices, Outstanding, Ending Balance	$ 17.43	$ 16.83	$ 16.51	$ 16.34	$ 17.43	$ 14.27
Weighted Average Remaining Life In Years, Ending Balance	4.0	4.0	4.2	4.4	4.0	4.3
Aggregate Intrinsic Value, Outstanding, Ending Balance	37	54	76	80	37	68
Shares Under Option, Vested and Expected to Vest, Ending Balance	2,700,577				2,700,577
Weighted Average Exercise prices, Vested and Expected to Vest, Ending Balance	$ 17.17				$ 17.17
Weighted Average Remaining Life in Years, Vested and Expected to Vest, Ending Balance	4.0				4.0
Aggregate Intrinsic Value, Vested and Expected to Vest, Ending balance	37				37
Share Under Options, Exercisable, Ending Balance	2,164,226				2,164,226
Weighted Average Exercise Prices, Exercisable, Ending Balance	$ 15.95				$ 15.95
Weighted Average Remaining Life in Years, Exercisable, Ending Balance	3.9				3.9
Aggregate Intrinsic Value, Exercisable Ending Balance	$ 30				$ 30