Investments (Details 11) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 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	$ 472		$ 472
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	118		118
Limited partnership impairment
Limited partnership interests	5,091		5,091		4,922
Write-downs of limited partnership	96	39	178	195
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	348		348
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	57		57
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	58		58
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	37		37
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	3		3
Limited partnership impairment
Write-downs of limited partnership	67	22	118	58
Equity-method limited partnerships
Limited partnership impairment
Limited partnership interests	3,660		3,660		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	$ 2	$ 2	$ 10	$ 5