Investments, Available-for-Sale Other Asset-backed Securities in Gross Unrealized Loss Position (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale Securities [Abstract]
Additional impairment losses	$ 0
Other Asset-Backed [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	133	$ 4
Estimated fair value	1,519	$ 482
Other Asset-Backed [Member] | AAA [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	1
Estimated fair value	49
Other Asset-Backed [Member] | AA [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	2
Estimated fair value	83
Other Asset-Backed [Member] | A [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	74
Estimated fair value	821
Other Asset-Backed [Member] | BBB [ Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	56
Estimated fair value	566
Other Asset-Backed [Member] | Auto [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	6
Estimated fair value	290
Other Asset-Backed [Member] | Franchise [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	39
Estimated fair value	414
Other Asset-Backed [Member] | Collateralized Loan Obligations [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	60
Estimated fair value	418
Other Asset-Backed [Member] | Other [Member]
Available-for-sale Securities [Abstract]
Gross unrealized losses	28
Estimated fair value	$ 397