Investments (excluding Consolidated Investment Entities) - Composition of US and Foreign Corporate Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	$ 44,366	$ 44,743
Fixed maturities, including securities pledged	48,329	47,394
Communications
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	2,587	2,765
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	341	258
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	4	17
Fixed maturities, including securities pledged	2,924	3,006
Financial
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	5,094	5,143
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	487	370
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	5	28
Fixed maturities, including securities pledged	5,576	5,485
Industrial and Other Companies
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	16,478	17,129
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	1,391	948
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	98	189
Fixed maturities, including securities pledged	17,771	17,888
Energy
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	4,268	4,509
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	459	310
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	45	75
Fixed maturities, including securities pledged	4,682	4,744
Utilities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	6,243	5,629
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	607	397
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	22	77
Fixed maturities, including securities pledged	6,828	5,949
Transportation
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	1,295	1,210
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	121	83
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	4	12
Fixed maturities, including securities pledged	1,412	1,281
U.S. and Foreign Corporate Securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost Basis	35,965	36,385
Fixed maturities, including securities pledged, Gross Unrealized Capital Gains	3,406	2,366
Fixed maturities, including securities pledged,Gross Unrealized Capital Losses	178	398
Fixed maturities, including securities pledged	$ 39,193	$ 38,353

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt 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 securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-Publisher FASB
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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
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Available-for-sale Securities, Including Securities Pledged [Line Items]

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