Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 60,705	$ 60,173
Gross Unrealized OTTI Loss	5	2
Debt Securities, Available-for-sale	62,279	64,991
Fixed maturity securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	60,705	60,173
Gross Unrealized Gain	2,867	5,180
Gross Unrealized Temporary Loss	1,298	365
Gross Unrealized OTTI Loss	(5)	(3)
Debt Securities, Available-for-sale	62,279	64,991
U.S. corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	23,475	21,190
Gross Unrealized Gain	918	1,859
Gross Unrealized Temporary Loss	458	92
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	23,935	22,957
U.S. government and agency
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	10,089	14,548
Gross Unrealized Gain	1,075	1,862
Gross Unrealized Temporary Loss	214	118
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	10,950	16,292
RMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	8,373	7,749
Gross Unrealized Gain	227	285
Gross Unrealized Temporary Loss	230	60
Gross Unrealized OTTI Loss	(4)	(3)
Debt Securities, Available-for-sale	8,374	7,977
Foreign corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	7,311	6,703
Gross Unrealized Gain	155	386
Gross Unrealized Temporary Loss	218	66
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	7,248	7,023
State and political subdivision
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	3,747	3,635
Gross Unrealized Gain	369	553
Gross Unrealized Temporary Loss	47	6
Gross Unrealized OTTI Loss	0	1
Debt Securities, Available-for-sale	4,069	4,181
CMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	4,381	3,386
Gross Unrealized Gain	9	53
Gross Unrealized Temporary Loss	101	17
Gross Unrealized OTTI Loss	(1)	(1)
Debt Securities, Available-for-sale	4,290	3,423
ABS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	2,006	1,810
Gross Unrealized Gain	10	21
Gross Unrealized Temporary Loss	7	2
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	2,009	1,829
Foreign government
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,323	1,152
Gross Unrealized Gain	104	161
Gross Unrealized Temporary Loss	23	4
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	$ 1,404	$ 1,309

Other-than-temporary impairments on fixed maturity securities transferred to other comprehensive income loss.

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- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 320
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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