General (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale Equity Securities, Unrealized Gain (Loss) Included in Other Comprehensive Income	$ 325	$ 276
Limited partnership interests	5,091	4,874
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for sale Equity Securities, Unrealized Gain (Loss) Included in Other Comprehensive Income	325
EMA limited partnerships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests	3,900	$ 3,720
EMA limited partnerships | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Limited partnership interests	$ 240