Investments (Details 11) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 302
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	220
Limited partnerships
Limited partnership interests	2,295	$ 2,024
Equity method limited partnerships
Limited partnerships
Limited partnership interests	1,770	1,520
Fixed income and equity securities
Other details of unrealized loss
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	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	163
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	102
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	98
Available for sale Securities, Unrealized Losses Having Loss of Less than Twenty Percent, Less than 12 Months	70
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	99
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	12
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	41
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	19
Carrying value
Limited partnerships
Cost method limited partnerships	530	508
Carrying value | Cost method limited partnership interests
Limited partnerships
Cost method limited partnerships	$ 530	$ 508