Investments, Available-for-Sale Corporate and Other Bonds in Gross Unrealized Loss Position (Details) - Corporate and Other Bonds [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale Securities [Abstract]
Gross unrealized losses	$ 817	$ 32
Estimated fair value	7,080	$ 1,100
AAA [Member]
Available-for-sale Securities [Abstract]
Estimated fair value	8
AA [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	4
Estimated fair value	134
A [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	17
Estimated fair value	608
BBB [ Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	516
Estimated fair value	4,987
Below Investment Grade [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	280
Estimated fair value	1,343
Basic Materials [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	78
Estimated fair value	727
Communications [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	27
Estimated fair value	349
Consumer, Cyclical - Other [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	56
Estimated fair value	390
Consumer, Non-cyclical - Other [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	27
Estimated fair value	401
Energy - Oil & Gas [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	191
Estimated fair value	575
Energy - Pipelines [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	112
Estimated fair value	523
Entertainment [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	23
Estimated fair value	148
Financial -Other [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	89
Estimated fair value	1,711
Financial - Real Estate/REITS [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	45
Estimated fair value	599
Industrial [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	55
Estimated fair value	468
Retail [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	18
Estimated fair value	150
Technology [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	30
Estimated fair value	290
Transportation [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	5
Estimated fair value	73
Travel & Related [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	37
Estimated fair value	269
Utilities [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	24
Estimated fair value	$ 407