Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) - Fair Value Decline, Greater Than 20% [Member] $ in Millions	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months	$ 174	$ 15
Fair Value - Six months or greater, but less than nine months	131	10
Fair Value - Twelve months or greater	30	132
Fair Value - Total	335	157
Gross Unrealized Losses - Less than six months	63	5
Gross Unrealized Losses - Six months or greater, but less than nine months	55	3
Gross Unrealized Losses - Twelve months or greater	13	76
Gross Unrealized Losses - Total	$ 131	$ 84
Number of Securities - Less than six months | security	27	7
Number of Securities - Six months or greater, but less than nine months | security	23	4
Number of Securities - Twelve months or greater | security	22	31
Number of Securities - Total | security	72	42