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 amortized cost or cost	$ 297		$ 297
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	100		100
Limited partnerships
Limited partnership interests	2,044		2,044		1,924
Write-downs of limited partnership	25	9	41	51
Equity method limited partnerships
Limited partnerships
Limited partnership interests	1,440		1,440		1,310
Write-downs of limited partnership	0	0	0	0
Cost method limited partnership interests
Limited partnerships
Limited partnership interests	603		603		617
Write-downs of limited partnership	1	0	5	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	244		244
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	56		56
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	44		44
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	$ 30		$ 30