Investments (Details 12) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 196
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	176
Limited partnership interests	2,405	$ 2,295
Equity method limited partnerships
Other details of unrealized loss
Limited partnership interests	1,860	1,770
Fixed income and equity securities
Other details of unrealized loss
Available for sale Securities Unrealized Losses	(372)	(522)
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	84
Available for sale Securities Unrealized Losses	(145)	(265)
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	61
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	42
Below Investment Grade Equity Securities [Member]
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	93
Below 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	70
Available for sale Securities Unrealized Losses	(163)	(197)
Available for sale Securities, Unrealized Losses Having Loss of Less than Twenty Percent, Less than 12 Months	43
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	22
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	14
Carrying value | Cost method limited partnership interests
Other details of unrealized loss
Limited partnership interests	$ 549	$ 530