Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	$ 17,198	$ 16,226	$ 15,738
Less: investment expenses	(763)	(706)	(909)
Net investment income	16,435	15,520	14,829
Trading account assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	920	986	1,205
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	2,267	2,243	2,255
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	617	627	619
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	203	145	56
Other long-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	1,117	731	717
Available-for-sale \| Fixed Maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	11,482	10,920	10,347
Available-for-sale \| Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	377	366	337
Held-to-maturity \| Fixed Maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income	$ 215	$ 208	$ 202

Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-16(Column G))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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