Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of Securities - Total | security		672	3,360
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 44	$ 389
Fair Value - Six months or greater, but less than nine months		5	96
Fair Value - Nine months or greater, but less than twelve months		10	11
Fair Value - Twelve months or greater		163	138
Fair Value - Total		222	634
Losses - Less than six months		19	122
Losses - Six months or greater, but less than nine months		2	49
Losses - Nine months or greater, but less than twelve months		5	8
Losses - Twelve months or greater		93	70
Gross Unrealized Losses - Total		119	249
OTTI - Less than six months			1
OTTI - Twelve months or greater		8	8
OTTI - Total		$ 8	$ 9
Number of Securities - Less than six months | security	[1]	11	44
Number of Securities - Six months or greater, but less than nine months | security	[1]	1	11
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	3	2
Number of Securities - Twelve months or greater | security	[1]	35	32
Number of Securities - Total | security	[1]	50	89

[1] We may reflect a security in more than one aging category based on various purchase dates.