Fair Value Measurements (details) (USD $)	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010
Fair Value Measurements disclosure
Percent of fixed maturities for which a pricing service estimates fair value	98.00%
Investment in non-public common and preferred equity securities where the fair value estimate is determined either internally or by an external fund manager	$ 45,000,000	$ 57,000,000
Convertible bonds held containing embedded conversion options that are valued separately from the host bond contract	28,000,000	37,000,000
Municipal fixed maturity securities valued using observable market data	81,000,000
Carrying value of financial instruments classified as other assets	547,000,000	647,000,000
Carrying value of financial instruments classified as other liabilities	3,950,000,000	3,750,000,000
Debt, carrying value	6,604,000,000	6,611,000,000
Debt, fair value	$ 7,350,000,000	$ 7,210,000,000
Percent of debt, other than commercial paper, for which a pricing service estimates fair value	96.00%	94.00%