Investments (Details 11) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 176
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	146
Limited partnerships
Limited partnership interests	1,933		1,924
Write-downs of limited partnership	1	33
Equity method limited partnerships
Limited partnerships
Limited partnership interests	1,320		1,310
Cost method limited partnership interests
Limited partnerships
Limited partnership interests	613		617
Write-downs of limited partnership	0	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	134
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	46
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	100
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	$ 96