Segments - Total Assets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Assets	$ 218,622.2	$ 218,223.5
Parent | Retirement
Segment Reporting Information [Line Items]
Assets	100,933.3	93,771.5
Parent | Investment Management
Segment Reporting Information [Line Items]
Assets	487.8	556.8
Parent | Annuities
Segment Reporting Information [Line Items]
Assets	25,852.7	25,055.7
Parent | Individual Life
Segment Reporting Information [Line Items]
Assets	27,403.8	26,068.9
Parent | Employee Benefits
Segment Reporting Information [Line Items]
Assets	2,653.6	2,554.8
Parent | Total Ongoing Businesses
Segment Reporting Information [Line Items]
Assets	157,331.2	148,007.7
Parent | Corporate
Segment Reporting Information [Line Items]
Assets	4,487.7	5,893.1
Parent | Closed Blocks
Segment Reporting Information [Line Items]
Assets	52,864.8	52,567.4
Parent | Closed Blocks | Closed Block Variable Annuity
Segment Reporting Information [Line Items]
Assets	45,234.4	44,322.9
Parent | Closed Blocks | Closed Block Other
Segment Reporting Information [Line Items]
Assets	7,630.4	8,244.5
Parent | Total Segment
Segment Reporting Information [Line Items]
Assets	214,683.7	206,468.2
Noncontrolling Interest
Segment Reporting Information [Line Items]
Assets	$ 3,938.5	$ 11,755.3