Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	$ 58,599	$ 57,289
Cost or Amortized Cost	212	280
Gross Unrealized OTTI Loss	2	1	$ (23)
Available-for-sale Securities, Debt Securities	63,333	59,899
Available-for-sale Securities, Equity Securities	232	300
Fixed maturity securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	58,599	57,289
Gross Unrealized Gain	5,083	3,532
Gross Unrealized Temporary Loss	352	923
Gross Unrealized OTTI Loss	(3)	(1)
Available-for-sale Securities, Debt Securities	63,333	59,899
U.S. corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	20,647	20,663
Gross Unrealized Gain	1,822	1,287
Gross Unrealized Temporary Loss	89	285
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	22,380	21,665
U.S. government and agency
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	14,185	11,872
Gross Unrealized Gain	1,844	1,281
Gross Unrealized Temporary Loss	116	237
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	15,913	12,916
RMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,588	7,876
Gross Unrealized Gain	283	203
Gross Unrealized Temporary Loss	57	139
Gross Unrealized OTTI Loss	(3)	0
Available-for-sale Securities, Debt Securities	7,817	7,940
Foreign corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	6,457	6,071
Gross Unrealized Gain	376	220
Gross Unrealized Temporary Loss	62	168
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	6,771	6,123
State and political subdivision
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,573	3,520
Gross Unrealized Gain	532	376
Gross Unrealized Temporary Loss	6	38
Gross Unrealized OTTI Loss	1	0
Available-for-sale Securities, Debt Securities	4,098	3,858
CMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,259	3,687
Gross Unrealized Gain	48	40
Gross Unrealized Temporary Loss	17	32
Gross Unrealized OTTI Loss	(1)	(1)
Available-for-sale Securities, Debt Securities	3,291	3,696
ABS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	1,779	2,600
Gross Unrealized Gain	19	11
Gross Unrealized Temporary Loss	2	13
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	1,796	2,598
Foreign government
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	1,111	1,000
Gross Unrealized Gain	159	114
Gross Unrealized Temporary Loss	3	11
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	1,267	1,103
Equity securities
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	212	280
Gross Unrealized Gain	21	29
Gross Unrealized Temporary Loss	1	9
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Equity Securities	$ 232	$ 300

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

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- Definition

Other-than-temporary impairments on equity securities transferred to other comprehensive loss.

+ References

No definition available.

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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
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-Publisher FASB
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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 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 debt securities categorized neither as held-to-maturity nor trading.

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