Investments (Details 11) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 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	$ 459		$ 459
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	122		122
Limited partnerships
Limited partnership interests	1,946		1,946		1,924
Write-downs of limited partnership	15	9	16	42
Equity method limited partnerships
Limited partnerships
Limited partnership interests	1,340		1,340		1,310
Write-downs of limited partnership	0	0	0	0
Cost method limited partnership interests
Limited partnerships
Limited partnership interests	611		611		617
Write-downs of limited partnership	4	1	4	2
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	387		387
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	59		59
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	63		63
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	48		48
Equity securities
Limited partnerships
Write-downs of limited partnership	$ 1		$ 1