Schedule I-Parent Company Financial Information (Parenthetical) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule I- Parent Company Financial Information [Abstract]
Preferred stock, par	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Common stock, par	$ 0.17	$ 0.17
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	193,230,310	190,244,741
Treasury stock, shares	29,225,996	21,795,051
Net unrealized investment gains, tax expense	$ 109	$ 47	$ 131
Reclassification adjustment for net realized gains included in net income, tax expense	$ 4	$ 2	$ 7