Investments (Equity Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,476	$ 1,440
Percentage of Equity Securities	100.00%	100.00%
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,476	$ 1,440
Common Stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,067	$ 1,037
Percentage of Equity Securities	72.30%	72.00%
Non-redeemable Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 409	$ 403
Percentage of Equity Securities	27.70%	28.00%