Investments (excluding Consolidated Investment Entities) - Mortgages by Year of Origination (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Total Commercial mortgage loans	$ 8,689	$ 8,006
2017
Investment [Line Items]
Total Commercial mortgage loans	1,525	0
2016
Investment [Line Items]
Total Commercial mortgage loans	1,428	1,434
2015
Investment [Line Items]
Total Commercial mortgage loans	1,250	1,286
2014
Investment [Line Items]
Total Commercial mortgage loans	1,303	1,333
2013
Investment [Line Items]
Total Commercial mortgage loans	1,287	1,371
2012
Investment [Line Items]
Total Commercial mortgage loans	818	1,084
2011 and prior
Investment [Line Items]
Total Commercial mortgage loans	$ 1,078	$ 1,498

Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5066-111524

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant