Investments (Details 11) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	$ 299
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	265
Limited partnership impairment
Limited partnership interests	4,922	4,697
Write-downs of limited partnership	239	563	937
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	192
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	64
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	187
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	176
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	14
Limited partnership impairment
Write-downs of limited partnership	75	139	57
Equity-method limited partnerships
Limited partnership impairment
Limited partnership interests	3,520	3,130
Write-downs of limited partnership		2	1
Cost-method limited partnership interests
Limited partnership impairment
Limited partnership interests	1,410	1,570
Write-downs of limited partnership	$ 8	$ 4	$ 45