Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Jun. 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		$ 32,167	$ 5,844
Fair Value - Twelve months or greater		5,590	6,063
Fair Value - Total		37,757	11,907
Losses - Nine months or greater, but less than twelve months		1,130	89
Losses - Twelve months or greater		620	374
Losses - Total		$ 1,750	$ 463
Number of Securities - Total | security		3,092	1,128
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 173	$ 156
Fair Value - Six months or greater, but less than nine months		39	2
Fair Value - Nine months or greater, but less than twelve months		7	15
Fair Value - Twelve months or greater		117	215
Fair Value - Total		336	388
Losses - Less than six months		59	57
Losses - Six months or greater, but less than nine months		16	1
Losses - Nine months or greater, but less than twelve months		4	8
Losses - Twelve months or greater		47	78
Losses - Total		126	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]	23	26
Number of Securities - Six months or greater, but less than nine months | security	[1]	6	4
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	1	7
Number of Securities - Twelve months or greater | security	[1]	28	49
Number of Securities - Total | security	[1]	58	86

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