Common Equity (Details 1) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock option activity
Outstanding, Shares, Beginning Balance	10,638,750.0
Outstanding, Weighted-Average Exercise Price, Beginning	$ 21.65
Granted, shares	938,770.0
Granted, Weighted-Average Exercise Price		$ 3.17	$ 3.36	$ 4.01
Outstanding, Shares, Ending Balance		10,638,750.0
Outstanding, Weighted-Average Exercise Price, Ending		$ 21.65
Outstanding, Weighted-Average Remaining Contractual Life (Years)		5.4
Exercisable, shares		7,534,980.0
Exercisable, Weighted-Average Exercise Price		$ 21.14
Exercisable, Weighted-Average Remaining Contractual Life (Years)		4.5
Stock options [Member]
Stock option activity
Outstanding, Shares, Beginning Balance		13,036,466.0
Outstanding, Weighted-Average Exercise Price, Beginning		$ 20.81
Granted, shares		458,180.0
Granted, Weighted-Average Exercise Price		$ 29.35
Exercised, shares		(2,855,896.0)
Exercised, Weighted-Average Exercise Price		$ 19.07
Forfeited, shares		0.0
Forfeited, Weighted-Average Exercise Price		$ 0.00
Outstanding, Shares, Ending Balance		10,638,750.0
Outstanding, Weighted-Average Exercise Price, Ending		$ 21.65
Outstanding, Weighted-Average Remaining Contractual Life (Years)		5.4
Outstanding, Aggregate Intrinsic Value		$ 141.6
Exercisable, shares		7,534,980.0
Exercisable, Weighted-Average Exercise Price		$ 21.14
Exercisable, Weighted-Average Remaining Contractual Life (Years)		4.5
Exercisable, Aggregate Intrinsic Value		$ 104.1