Investments (Current and Long-term Equity Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Equity Securities	$ 1,525	$ 1,526
Exchange Traded Funds [Member]
Investment [Line Items]
Equity Securities	510	2
Fixed Maturity Mutual Funds [Member]
Investment [Line Items]
Equity Securities	633	557
Common Equity Securities [Member]
Investment [Line Items]
Equity Securities	77	654
Private Equity Securities [Member]
Investment [Line Items]
Equity Securities	$ 305	$ 313