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 cost or amortized cost	$ 754		$ 754
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	141		141
Limited partnership impairment
Limited partnership interests	4,941		4,941		4,922
Write-downs of limited partnership	55	69	82	156
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	549		549
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized 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 cost or amortized cost	78		78
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	55		55
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	4		4
Limited partnership impairment
Write-downs of limited partnership	32	20	51	36
Equity-method limited partnerships
Limited partnership impairment
Limited partnership interests	3,500		3,500		3,520
Write-downs of limited partnership	0	0	0	0
Cost-method limited partnership interests
Limited partnership impairment
Limited partnership interests	1,440		1,440		1,410
Write-downs of limited partnership	$ 8	$ 1	$ 8	$ 3