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	$ 59,072	$ 58,599
Gross Unrealized OTTI Loss	5	2
Debt Securities, Available-for-sale	60,627	63,333
Fixed maturity securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	59,072	58,599
Gross Unrealized Gain	2,817	5,083
Gross Unrealized Temporary Loss	1,267	352
Gross Unrealized OTTI Loss	(5)	(3)
Debt Securities, Available-for-sale	60,627	63,333
U.S. corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	22,957	20,647
Gross Unrealized Gain	899	1,822
Gross Unrealized Temporary Loss	452	89
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	23,404	22,380
U.S. government and agency
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,647	14,185
Gross Unrealized Gain	1,067	1,844
Gross Unrealized Temporary Loss	209	116
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	10,505	15,913
RMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	8,199	7,588
Gross Unrealized Gain	225	283
Gross Unrealized Temporary Loss	221	57
Gross Unrealized OTTI Loss	(4)	(3)
Debt Securities, Available-for-sale	8,207	7,817
Foreign corporate
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	7,103	6,457
Gross Unrealized Gain	151	376
Gross Unrealized Temporary Loss	209	62
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	7,045	6,771
State and political subdivision
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	3,683	3,573
Gross Unrealized Gain	354	532
Gross Unrealized Temporary Loss	47	6
Gross Unrealized OTTI Loss	0	1
Debt Securities, Available-for-sale	3,990	4,098
CMBS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	4,235	3,259
Gross Unrealized Gain	8	48
Gross Unrealized Temporary Loss	99	17
Gross Unrealized OTTI Loss	(1)	(1)
Debt Securities, Available-for-sale	4,145	3,291
ABS
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,976	1,779
Gross Unrealized Gain	10	19
Gross Unrealized Temporary Loss	8	2
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	1,978	1,796
Foreign government
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,272	1,111
Gross Unrealized Gain	103	159
Gross Unrealized Temporary Loss	22	3
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	$ 1,353	$ 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
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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

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-Publisher FASB
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-Topic 320
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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)
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