Investments (Details 12) - USD ($) $ in Millions	Sep. 30, 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	$ 75
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	79
Limited partnership interests	2,679	$ 2,295
Equity method limited partnerships
Other details of unrealized loss
Limited partnership interests	2,050	1,770
Fixed income and equity securities
Other details of unrealized loss
Available for sale Securities Unrealized Losses	(154)	(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	29
Available for sale Securities Unrealized Losses	(63)	(265)
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	34
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	24
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	27
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	22
Available for sale Securities Unrealized Losses	(49)	(197)
Available for sale Securities, Unrealized Losses Having Loss of Less than Twenty Percent, Less than 12 Months	7
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	18
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	$ 632	$ 530