Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale Securities [Abstract]
Amortized Cost	$ 58,460	$ 58,599
Gross Unrealized OTTI Loss	2	2
Available-for-sale Securities, Debt Securities	61,560	63,333
Fixed maturity securities
Available-for-sale Securities [Abstract]
Amortized Cost	58,460	58,599
Gross Unrealized Gain	3,922	5,083
Gross Unrealized Temporary Loss	825	352
Gross Unrealized OTTI Loss	(3)	(3)
Available-for-sale Securities, Debt Securities	61,560	63,333
U.S. corporate
Available-for-sale Securities [Abstract]
Amortized Cost	21,644	20,647
Gross Unrealized Gain	1,320	1,822
Gross Unrealized Temporary Loss	276	89
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	22,688	22,380
U.S. government and agency
Available-for-sale Securities [Abstract]
Amortized Cost	12,367	14,185
Gross Unrealized Gain	1,448	1,844
Gross Unrealized Temporary Loss	219	116
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	13,596	15,913
RMBS
Available-for-sale Securities [Abstract]
Amortized Cost	7,645	7,588
Gross Unrealized Gain	250	283
Gross Unrealized Temporary Loss	150	57
Gross Unrealized OTTI Loss	(2)	(3)
Available-for-sale Securities, Debt Securities	7,747	7,817
Foreign corporate
Available-for-sale Securities [Abstract]
Amortized Cost	6,477	6,457
Gross Unrealized Gain	288	376
Gross Unrealized Temporary Loss	91	62
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	6,674	6,771
State and political subdivision
Available-for-sale Securities [Abstract]
Amortized Cost	3,567	3,573
Gross Unrealized Gain	459	532
Gross Unrealized Temporary Loss	18	6
Gross Unrealized OTTI Loss	0	1
Available-for-sale Securities, Debt Securities	4,008	4,098
CMBS
Available-for-sale Securities [Abstract]
Amortized Cost	3,752	3,259
Gross Unrealized Gain	16	48
Gross Unrealized Temporary Loss	57	17
Gross Unrealized OTTI Loss	(1)	(1)
Available-for-sale Securities, Debt Securities	3,712	3,291
ABS
Available-for-sale Securities [Abstract]
Amortized Cost	1,854	1,779
Gross Unrealized Gain	18	19
Gross Unrealized Temporary Loss	3	2
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	1,869	1,796
Foreign government
Available-for-sale Securities [Abstract]
Amortized Cost	1,154	1,111
Gross Unrealized Gain	123	159
Gross Unrealized Temporary Loss	11	3
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	$ 1,266	$ 1,267

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

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- Definition

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

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