Investments (Details 12) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	$ (411)
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	(89)
Limited partnership interests	4,536	$ 4,527
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	(195)
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	(32)
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	(49)
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	6
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 cost or amortized cost	(8)
Equity-method limited partnerships
Other details of unrealized loss
Limited partnership interests	3,410	3,410
Carrying value
Other details of unrealized loss
Cost Method Investments	1,130	1,122
Carrying value | Cost-method Investments
Other details of unrealized loss
Cost Method Investments	$ 1,130	$ 1,120