Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain (Loss) on Investments [Line Items]
Fixed maturities, fair value of hybrid securities	$ 31
Fixed maturity investments, Percentage of amortized costs	70.00%	70.00%
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	1	5
Investments, deposit with various states	85
Investments in fair value, deposit with various states	13,164	12,371
Impaired securities	13	12	15
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	874	713
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	1	5	4
Number of securities total unrealized loss in an unrealized loss position for 12 months or more	4	20	17
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	1,014	829
Investments securities total unrealized loss in an unrealized loss position for 12 months or more			1
Number of securities total unrealized loss in an unrealized loss position for 12 months or more			3
Equity Securities [Member] | Maximum [Member]
Gain (Loss) on Investments [Line Items]
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	1
Procter And Gamble Company, Exxon Mobile Corporation And Chevron Corporation [Member]
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	282
Three Primary Contributors
Gain (Loss) on Investments [Line Items]
Number of securities	3
On Deposit With Various States
Gain (Loss) on Investments [Line Items]
Investments in fair value, deposit with various states	$ 93