Investments - Total unrealized losses and limited partnerships narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other details of unrealized loss
Unrealized losses related to securities with unrealized loss position less than 20% of amortized cost or cost	$ 358
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	31
Limited partnerships
Limited partnership interests	3,292	$ 3,147
Equity method limited partnerships
Limited partnerships
Limited partnership interests	2,510	2,540
Fixed income and equity securities
Other details of unrealized loss
Available-for-sale securities, continuous unrealized loss position, accumulated loss	389
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	252
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	16
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	106
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	93
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost	15
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	2
Carrying value | Cost method limited partnership interests
Limited partnerships
Limited partnership interests	$ 787	$ 611