Long-Term Debt (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended	6 Months Ended	9 Months Ended				12 Months Ended
	Dec. 31, 2011 days	Jun. 30, 2006 June 2006 hybrids [Member]	Sep. 30, 2006 September 2006 hybrids [Member]	Dec. 31, 2011 September 2006 hybrids [Member]	Apr. 30, 2010 September 2006 hybrids [Member]	Jun. 30, 2009 June 2009 hybrids [Member]	Dec. 31, 2011 Junior Subordinated Debt [Member]	Dec. 31, 2010 Junior Subordinated Debt [Member]	Dec. 31, 2009 Junior Subordinated Debt [Member]
Interest Expense, Debt							$ 21	$ 21	$ 21
Outstanding contingent convertible senior notes	143
Conversion rate (shares)	27.173
Common stock principal amount of senior notes (per share)	$ 1,000
Conversion price (per share)	$ 36.80
Conversion rate adjustment (shares)	$ 28.9178
Minimum consecutive trading days	20
Maximum consecutive trading days	30
Convertible senior notes converted by holders	59
Common stock, closing price equal (per share)	$ 41.50
Average trading price principal amount of the senior notes	120.00%
Redemption Rate	100.00%
Noncontrolling interest, ownership percentage by parent	100.00%
Beneficial ownership percentage	97.00%
Beneficial ownership interest	3.00%
Percentage in capital trust assets	100.00%
Junior subordinated notes		300	500			685
Underwriter option to purchase additional notes to cover over-allotments						60
Debt instrument, interest rate		7.50%	6.30%			8.375%
Interest bear on junior subordinated notes		2.825%	2.3%
Defer interest payments on the hybrids	10
Purchased and cancelled of junior subordinated notes				$ 16	$ 16