Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Mar. 31, 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		$ 22,188	$ 5,844
Fair Value - Twelve months or greater		5,672	6,063
Fair Value - Total		27,860	11,907
Losses - Nine months or greater, but less than twelve months		549	89
Losses - Twelve months or greater		524	374
Losses - Total		$ 1,073	$ 463
Number of Securities - Total | security		2,208	1,128
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 102	$ 156
Fair Value - Six months or greater, but less than nine months		17	2
Fair Value - Nine months or greater, but less than twelve months			15
Fair Value - Twelve months or greater		182	215
Fair Value - Total		301	388
Losses - Less than six months		33	57
Losses - Six months or greater, but less than nine months		8	1
Losses - Nine months or greater, but less than twelve months			8
Losses - Twelve months or greater		63	78
Losses - Total		104	144
OTTI - Less than six months		2	1
OTTI - Twelve months or greater		8	10
OTTI - Total		$ 10	$ 11
Number of Securities - Less than six months | security	[1]	18	26
Number of Securities - Six months or greater, but less than nine months | security	[1]	4	4
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	3	7
Number of Securities - Twelve months or greater | security	[1]	30	49
Number of Securities - Total | security	[1]	55	86

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