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 cost or amortized cost	$ 161
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	111
Limited partnership interests	5,588	$ 4,874
Fixed income and equity securities
Other details of unrealized loss
Unrealized losses	272	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	44
Unrealized losses	78	467
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	34
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	53
Unrealized losses	90	493
Unrealized losses having loss of less than twenty percent, less than 12 months	23
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	37
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	20
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	40
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	64
Unrealized losses	104	139
Equity-method limited partnerships
Other details of unrealized loss
Limited partnership interests	4,210	3,720
Carrying value
Other details of unrealized loss
Cost method limited partnerships	1,375	1,154
Carrying value | Cost-method Investments
Other details of unrealized loss
Cost method limited partnerships	$ 1,380	$ 1,150