Investments (Equity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,432	$ 1,440
Percentage of Equity Securities	100.00%	100.00%
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,432	$ 1,440
Common Stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,016	$ 1,037
Percentage of Equity Securities	70.90%	72.00%
Non-redeemable Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 416	$ 403
Percentage of Equity Securities	29.10%	28.00%