Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 58,523	$ 58,599
Gross Unrealized OTTI Loss	6	2
Debt Securities, Available-for-sale	60,753	63,333
Fixed maturity securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	58,523	58,599
Gross Unrealized Gain	3,343	5,083
Gross Unrealized Temporary Loss	1,120	352
Gross Unrealized OTTI Loss	(7)	(3)
Debt Securities, Available-for-sale	60,753	63,333
U.S. corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	22,439	20,647
Gross Unrealized Gain	963	1,822
Gross Unrealized Temporary Loss	439	89
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	22,963	22,380
U.S. government and agency
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	10,871	14,185
Gross Unrealized Gain	1,397	1,844
Gross Unrealized Temporary Loss	190	116
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	12,078	15,913
RMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	7,615	7,588
Gross Unrealized Gain	249	283
Gross Unrealized Temporary Loss	173	57
Gross Unrealized OTTI Loss	(4)	(3)
Debt Securities, Available-for-sale	7,695	7,817
Foreign corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	6,751	6,457
Gross Unrealized Gain	171	376
Gross Unrealized Temporary Loss	176	62
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	6,746	6,771
State and political subdivision
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	3,583	3,573
Gross Unrealized Gain	435	532
Gross Unrealized Temporary Loss	25	6
Gross Unrealized OTTI Loss	(2)	1
Debt Securities, Available-for-sale	3,995	4,098
CMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	3,967	3,259
Gross Unrealized Gain	10	48
Gross Unrealized Temporary Loss	87	17
Gross Unrealized OTTI Loss	(1)	(1)
Debt Securities, Available-for-sale	3,891	3,291
ABS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	2,041	1,779
Gross Unrealized Gain	14	19
Gross Unrealized Temporary Loss	5	2
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	2,050	1,796
Foreign government
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,256	1,111
Gross Unrealized Gain	104	159
Gross Unrealized Temporary Loss	25	3
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	$ 1,335	$ 1,267

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
-Paragraph 2
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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
-Name Accounting Standards Codification
-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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