Investments (Details 11) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 251		$ 251
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	277		277
Limited partnerships
Limited partnership interests	1,860		1,860		1,612
Write-downs of limited partnership	9	84	51	207
Equity method limited partnerships
Limited partnerships
Limited partnership interests	1,230		1,230		858
Cost method limited partnership interests
Limited partnerships
Limited partnership interests	631		631		754
Write-downs of limited partnership			2	1
Investment grade fixed income securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	192		192
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	91		91
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 amortized cost or cost	186		186
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	$ 174		$ 174