Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of Securities - Total | security		895
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months	$ 1,528	$ 15
Fair Value - Six months or greater, but less than nine months		10
Fair Value - Twelve months or greater	50	132
Fair Value - Total	1,578	157
Gross Unrealized Losses - Less than six months	803	5
Gross Unrealized Losses - Six months or greater, but less than nine months		3
Gross Unrealized Losses - Twelve months or greater	60	76
Gross Unrealized Losses - Total	$ 863	$ 84
Number of Securities - Less than six months | security	185	7
Number of Securities - Six months or greater, but less than nine months | security		4
Number of Securities - Twelve months or greater | security	23	31
Number of Securities - Total | security	208	42