Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		Sep. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Nine months or greater, but less than twelve months		$ 9,089	$ 17,813
Fair Value - Twelve months or greater		2,760	4,155
Fair Value - Total		11,849	21,968
Fair Value		94,069	89,488
Losses - Nine months or greater, but less than twelve months		258	659
Losses - Twelve months or greater		274	507
Losses - Total		$ 532	$ 1,166
Number of Securities - Total | security		1,052	1,744
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 43	$ 174
Fair Value - Six months or greater, but less than nine months		15
Fair Value - Nine months or greater, but less than twelve months		32	1
Fair Value - Twelve months or greater		229	364
Fair Value - Total		319	539
Losses - Less than six months		18	52
Losses - Six months or greater, but less than nine months		7
Losses - Nine months or greater, but less than twelve months		10	1
Losses - Twelve months or greater		84	167
Losses - Total		119	220
OTTI - Less than six months			2
OTTI - Twelve months or greater		10	10
OTTI - Total		$ 10	$ 12
Number of Securities - Less than six months | security	[1]	17	19
Number of Securities - Six months or greater, but less than nine months | security	[1]	8
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	2	2
Number of Securities - Twelve months or greater | security	[1]	50	62
Number of Securities - Total | security	[1]	77	83

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