Investments (Details 12) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 70,000,000
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	33,000,000
Limited partnership interests	3,138,000,000	$ 2,776,000,000
Equity method limited partnerships
Other details of unrealized loss
Limited partnership interests	2,520,000,000	2,190,000,000
Fixed income and equity securities
Other details of unrealized loss
Available for sale securities unrealized losses	(103,000,000)	(235,000,000)
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	47,000,000
Available for sale securities unrealized losses	(63,000,000)	(147,000,000)
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	16,000,000
Equity securities
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	10,000,000
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	13,000,000
Available for sale securities unrealized losses	(24,000,000)	(53,000,000)
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	8,000,000
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	6,000,000
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 amortized cost or cost	11,000,000
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost for 12 months or more	0
Carrying value | Cost method limited partnership interests
Other details of unrealized loss
Limited partnership interests	$ 617,000,000	$ 591,000,000