General (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale equity securities, included in other comprehensive income		$ 966	$ 509
Limited partnership interests		6,600	5,814
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale equity securities, included in other comprehensive income		966
EMA limited partnerships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests		5,260	$ 4,530
EMA limited partnerships | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests		$ 200
Minimum | Scenario, Forecast | Accounting Standards Update 2016-20
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs, period increase	$ 145
Maximum | Scenario, Forecast | Accounting Standards Update 2016-20
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs, period increase	$ 175