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]
Cost or Amortized Cost	$ 287,099	$ 286,069
Gross Unrealized OTTI Loss	35	41
Available-for-sale Securities, Debt Securities	304,711	308,931
Equity securities	$ 1,544	$ 2,513
Percentage of Available-for-sale Equity Securities	100.00%	100.00%
Fixed Maturity Securities
Available-for-sale Securities [Abstract]
Gross Unrealized Gain	$ 21,045	$ 24,765
Gross Unrealized Temporary Loss	3,467	1,945
Gross Unrealized OTTI Loss	(34)	(42)
U.S. corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	77,786	76,005
Gross Unrealized Gain	5,105	7,007
Gross Unrealized Temporary Loss	1,057	351
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	81,834	82,661
U.S. government and agency
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	40,989	43,446
Gross Unrealized Gain	3,395	4,227
Gross Unrealized Temporary Loss	557	279
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	43,827	47,394
Foreign government
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	58,423	55,351
Gross Unrealized Gain	6,484	6,495
Gross Unrealized Temporary Loss	397	312
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	64,510	61,534
Foreign corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	52,894	52,409
Gross Unrealized Gain	3,366	3,836
Gross Unrealized Temporary Loss	797	676
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	55,463	55,569
RMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	26,858	27,846
Gross Unrealized Gain	999	1,145
Gross Unrealized Temporary Loss	481	233
Gross Unrealized OTTI Loss	(35)	(42)
Available-for-sale Securities, Debt Securities	27,411	28,800
State and political subdivision
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,762	10,752
Gross Unrealized Gain	1,473	1,717
Gross Unrealized Temporary Loss	43	13
Gross Unrealized OTTI Loss	0	1
Available-for-sale Securities, Debt Securities	12,192	12,455
ABS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	11,695	12,213
Gross Unrealized Gain	111	116
Gross Unrealized Temporary Loss	41	39
Gross Unrealized OTTI Loss	1	(1)
Available-for-sale Securities, Debt Securities	11,764	12,291
CMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,692	8,047
Gross Unrealized Gain	112	222
Gross Unrealized Temporary Loss	94	42
Gross Unrealized OTTI Loss	0	0
Available-for-sale Securities, Debt Securities	7,710	8,227
Equity Securities
Available-for-sale Securities [Abstract]
Equity securities	1,544	2,513
Common Stock
Available-for-sale Securities [Abstract]
Equity securities	$ 1,046	$ 2,035
Percentage of Available-for-sale Equity Securities	67.70%	81.00%
Non-redeemable preferred stock
Available-for-sale Securities [Abstract]
Equity securities	$ 498	$ 478
Percentage of Available-for-sale Equity Securities	32.30%	19.00%

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

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Percentage of Available-for-sale Equity Securities.

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+ 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)
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-Publisher FASB
-Name Accounting Standards Codification
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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