Investments (Details 12) - USD ($) $ in Millions	Sep. 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	$ 652
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	(267)
Limited partnership interests	4,823	$ 4,527
Fixed income and equity securities
Other details of unrealized loss
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	919	369
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	223
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	297	158
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	(74)
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	324
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	461	156
Available for sale Securities, Unrealized Losses Having Loss of Less than Twenty Percent, Less than 12 Months	276
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	(137)
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	10
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	(56)
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	105
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	161	55
Equity-method limited partnerships
Other details of unrealized loss
Limited partnership interests	3,680	3,410
Carrying value
Other details of unrealized loss
Cost Method Investments	1,148	1,122
Carrying value | Cost-method Investments
Other details of unrealized loss
Cost Method Investments	$ 1,150	$ 1,120