Investments Investments (Schedule Of Amortized Cost and Fair Value of Available-for-sale Securities and Related OTTI Recognized in AOCI) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	$ 78,546	$ 77,835
Available-for-sale,Gross Unrealized Gain	769	1,528
Available-for-sale, Gross Unrealized Depreciation	(1,352)	(424)
Available for sale, Fair Value	77,963	78,939
Available for sale, OTTI recognized in AOCI	(5)	(6)
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	3,827	3,701
Available-for-sale,Gross Unrealized Gain	18	32
Available-for-sale, Gross Unrealized Depreciation	(81)	(35)
Available for sale, Fair Value	3,764	3,698
Available for sale, OTTI recognized in AOCI	0	0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	21,884	20,514
Available-for-sale,Gross Unrealized Gain	421	622
Available-for-sale, Gross Unrealized Depreciation	(294)	(106)
Available for sale, Fair Value	22,011	21,030
Available for sale, OTTI recognized in AOCI	0	(1)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	24,665	23,453
Available-for-sale,Gross Unrealized Gain	235	638
Available-for-sale, Gross Unrealized Depreciation	(415)	(95)
Available for sale, Fair Value	24,485	23,996
Available for sale, OTTI recognized in AOCI	(4)	(4)
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	15,853	15,279
Available-for-sale,Gross Unrealized Gain	40	111
Available-for-sale, Gross Unrealized Depreciation	(410)	(100)
Available for sale, Fair Value	15,483	15,290
Available for sale, OTTI recognized in AOCI	(1)	(1)
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	12,317	14,888
Available-for-sale,Gross Unrealized Gain	55	125
Available-for-sale, Gross Unrealized Depreciation	(152)	(88)
Available for sale, Fair Value	12,220	14,925
Available for sale, OTTI recognized in AOCI	$ 0	$ 0

Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 9A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284427-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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