Investments (Schedule Of Available-For-Sale Securities Whose Value Is Below Amortized Cost) (Details) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value - Nine months or greater, but less than twelve months		$ 16,142	$ 17,813
Fair Value - Twelve months or greater		3,651	4,155
Fair Value - Total		19,793	21,968
Fair Value		91,378	89,488
Losses - Nine months or greater, but less than twelve months		553	659
Losses - Twelve months or greater		385	507
Losses - Total		$ 938	$ 1,166
Number of Securities - Total | security		1,584	1,744
Fair Value Decline, Greater Than 20% [Member]
Available For Sale Securities In Unrealized Loss Position With Loss Severity Greater Than 20 Percent [Line Items]
Fair Value - Less than six months		$ 92	$ 174
Fair Value - Six months or greater, but less than nine months		25
Fair Value - Nine months or greater, but less than twelve months			1
Fair Value - Twelve months or greater		265	364
Fair Value - Total		382	539
Losses - Less than six months		31	52
Losses - Six months or greater, but less than nine months		7
Losses - Nine months or greater, but less than twelve months			1
Losses - Twelve months or greater		105	167
Losses - Total		143	220
OTTI - Less than six months			2
OTTI - Six months or greater, but less than nine months		1
OTTI - Twelve months or greater		9	10
OTTI - Total		$ 10	$ 12
Number of Securities - Less than six months | security	[1]	18	19
Number of Securities - Six months or greater, but less than nine months | security	[1]	4
Number of Securities - Nine months or greater, but less than twelve months | security	[1]		2
Number of Securities - Twelve months or greater | security	[1]	52	62
Number of Securities - Total | security	[1]	74	83

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