Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Nine months or greater, but less than twelve months		$ 36,894	$ 5,844
Fair Value - Twelve months or greater		5,738	6,063
Fair Value - Total		42,632	11,907
Losses - Nine months or greater, but less than twelve months		1,287	89
Losses - Twelve months or greater		663	374
Losses - Total		$ 1,950	$ 463
Number of Securities - Total | security		3,480	1,128
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 131	$ 156
Fair Value - Six months or greater, but less than nine months		21	2
Fair Value - Nine months or greater, but less than twelve months		39	15
Fair Value - Twelve months or greater		123	215
Fair Value - Total		314	388
Losses - Less than six months		47	57
Losses - Six months or greater, but less than nine months		16	1
Losses - Nine months or greater, but less than twelve months		16	8
Losses - Twelve months or greater		50	78
Losses - Total		129	144
OTTI - Less than six months			1
OTTI - Twelve months or greater		8	10
OTTI - Total		$ 8	$ 11
Number of Securities - Less than six months | security	[1]	20	26
Number of Securities - Six months or greater, but less than nine months | security	[1]	3	4
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	4	7
Number of Securities - Twelve months or greater | security	[1]	29	49
Number of Securities - Total | security	[1]	56	86

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