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 cost or amortized cost	$ 220
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	177
Limited partnership impairment
Limited partnership interests	4,931		4,922
Write-downs of limited partnership	27	87
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	142
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	45
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	127
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	119
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	5
Limited partnership impairment
Write-downs of limited partnership	19	16
Equity-method limited partnerships
Limited partnership impairment
Limited partnership interests	3,510		3,520
Write-downs of limited partnership	0	0
Cost-method limited partnership interests
Limited partnership impairment
Limited partnership interests	1,430		1,410
Write-downs of limited partnership	$ 0	$ 2