Investments (Details 12) - USD ($) $ in Millions	Dec. 31, 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	$ 444
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	88
Limited partnership interests	5,814	$ 4,874
Fixed income and equity securities
Other details of unrealized loss
Available-for-sale securities, continuous unrealized loss position, accumulated loss	532	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	318
Available-for-sale securities, continuous unrealized loss position, accumulated loss	344	467
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	26
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of cost or amortized cost	55
Available-for-sale securities, continuous unrealized loss position, accumulated loss	85	139
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	30
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	71
Available-for-sale securities, continuous unrealized loss position, accumulated loss	103	493
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	47
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of cost or amortized cost	32
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	14
Equity-method limited partnerships
Other details of unrealized loss
Limited partnership interests	4,530	3,720
Cost-method limited partnership interests
Other details of unrealized loss
Limited partnership interests	$ 1,280	$ 1,150