General (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale equity securities, included in other comprehensive income	$ 341	$ 276
Limited partnership interests	5,407	4,874
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	341
EMA limited partnerships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests	4,120	$ 3,720
EMA limited partnerships | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests	$ 202