Segments - Total Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total assets	$ 222,532	$ 214,585
Total assets, excluding assets held for sale	163,480	151,876
Assets held for sale	59,052	62,709
Corporate
Segment Reporting Information [Line Items]
Total assets	18,685	18,391
Parent | Total Segment
Segment Reporting Information [Line Items]
Total assets	160,745	148,408
Consolidation of investment entities
Segment Reporting Information [Line Items]
Total assets	2,735	3,468
Operating Segments | Retirement
Segment Reporting Information [Line Items]
Total assets	111,476	100,104
Operating Segments | Investment Management
Segment Reporting Information [Line Items]
Total assets	626	513
Operating Segments | Individual Life
Segment Reporting Information [Line Items]
Total assets	27,301	26,851
Operating Segments | Employee Benefits
Segment Reporting Information [Line Items]
Total assets	$ 2,657	$ 2,549