Investments (Current and Long-term Equity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Equity Securities	$ 570	$ 1,009
Exchange Traded Funds [Member]
Marketable Securities [Line Items]
Equity Securities	245	44
Fixed Maturity Mutual Funds [Member]
Marketable Securities [Line Items]
Equity Securities	211	643
Common Equity Securities [Member]
Marketable Securities [Line Items]
Equity Securities	32	237
Private Equity Funds [Member]
Marketable Securities [Line Items]
Equity Securities	$ 82	$ 85