Investments (Details 12) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	$ 288
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	201
Limited partnership interests	5,407	$ 4,874
Fixed income and equity securities
Other details of unrealized loss
Unrealized losses	489	1,099
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	65
Unrealized losses	111	467
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	46
Below 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	144
Unrealized losses	213	493
Unrealized losses having loss of less than twenty percent, less than 12 months	76
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	69
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	18
Below Investment Grade 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	86
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	79
Unrealized losses	165	139
Equity-method limited partnerships
Other details of unrealized loss
Limited partnership interests	4,120	3,720
Carrying value
Other details of unrealized loss
Cost method limited partnerships	1,284	1,154
Carrying value | Cost-method Investments
Other details of unrealized loss
Cost method limited partnerships	$ 1,280	$ 1,150