Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 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		$ 10,065	$ 17,813
Fair Value - Twelve months or greater		3,063	4,155
Fair Value - Total		13,128	21,968
Fair Value		93,289	89,488
Losses - Nine months or greater, but less than twelve months		279	659
Losses - Twelve months or greater		339	507
Losses - Total		$ 618	$ 1,166
Number of Securities - Total | security		1,155	1,744
Fair Value Decline, Greater Than 20% [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less than six months		$ 64	$ 174
Fair Value - Six months or greater, but less than nine months		41
Fair Value - Nine months or greater, but less than twelve months		2	1
Fair Value - Twelve months or greater		253	364
Fair Value - Total		360	539
Losses - Less than six months		26	52
Losses - Six months or greater, but less than nine months		14
Losses - Nine months or greater, but less than twelve months		1	1
Losses - Twelve months or greater		110	167
Losses - Total		151	220
OTTI - Less than six months			2
OTTI - Nine months or greater, but less than twelve months		1
OTTI - Twelve months or greater		9	10
OTTI - Total		$ 10	$ 12
Number of Securities - Less than six months | security	[1]	21	19
Number of Securities - Six months or greater, but less than nine months | security	[1]	5
Number of Securities - Nine months or greater, but less than twelve months | security	[1]	3	2
Number of Securities - Twelve months or greater | security	[1]	51	62
Number of Securities - Total | security	[1]	80	83

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