Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Nine months or greater, but less than twelve months		$ 5,693	$ 33,630
Fair Value - Twelve months or greater		15,929	8,386
Fair Value - Total		21,622	42,016
Losses - Nine months or greater, but less than twelve months		168	1,521
Losses - Twelve months or greater		748	818
Gross Unrealized Losses - Total		$ 916	$ 2,339
Number of Securities - Total | security		1,847	3,360
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 23	$ 389
Fair Value - Six months or greater, but less than nine months		20	96
Fair Value - Nine months or greater, but less than twelve months		98	11
Fair Value - Twelve months or greater		147	138
Fair Value - Total		288	634
Losses - Less than six months		8	122
Losses - Six months or greater, but less than nine months		6	49
Losses - Nine months or greater, but less than twelve months		42	8
Losses - Twelve months or greater		50	70
Gross Unrealized Losses - Total		106	249
OTTI - Less than six months		1	1
OTTI - Twelve months or greater		20	8
OTTI - Total		$ 21	$ 9
Number of Securities - Less than six months | security	[1]	7	44
Number of Securities - Six months or greater, but less than nine months | security	[1]	4	11
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	10	2
Number of Securities - Twelve months or greater | security	[1]	32	32
Number of Securities - Total | security	[1]	53	89

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