Investments (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Gain (Loss) on Investments
Largest single common stock holding	$ 644	$ 414
Largest equity holdings to total equity portfolio	7.50%	5.50%
Largest equity holdings to total portfolio	3.00%	2.10%
Assets Held by Insurance Regulators	$ 121	$ 117
Collateral at fair value	98	$ 95
Impaired securities		3	1
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss		$ 3	$ 58
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	$ 8,856	$ 7,752
Number of Impaired Securities with Allowance for Credit Losses | security	0
Fixed Maturities
Gain (Loss) on Investments
Number of securities total unrealized loss in an unrealized loss position for 12 months or more		38	400
Number of securities below 70 percent of amortized cost	0	0	0
Number Of Impaired Securities Intended to be Sold | security	14
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss 3	$ 10
Number Of Securities Continuous Unrealized Loss Position | security	128
Equity Securities | Common Stock
Gain (Loss) on Investments
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	$ 8,541	$ 7,518