Investments (Details 11) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	$ 472		$ 472
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	766		766
Unrealized losses related to securities with unrealized loss position greater than 20% of cost or amortized cost, unrealized loss position of 12 or more consecutive months	400		400
Limited partnership impairment
Limited partnership interests	4,694		4,694		4,697
Write-downs of limited partnership	69	82	156	238
Fixed income securities
Limited partnership impairment
Write-downs of limited partnership	46	60	114	188
Investment grade fixed income securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	262		262
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	231		231
Below investment grade fixed income securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	484		484
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	51		51
Limited partnership impairment
Write-downs of limited partnership	20	13	36	33
Equity-method limited partnerships
Limited partnership impairment
Limited partnership interests	3,330		3,330		3,130
Cost-method limited partnership interests
Limited partnership impairment
Limited partnership interests	1,360		1,360		1,570
Write-downs of limited partnership	$ 1	$ 1	$ 3	$ 2