Goodwill and Other Intangible Assets - Changes in Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Changes in Goodwill
Beginning balance, Goodwill	$ 1,100.0	$ 1,068.8
Goodwill from acquisitions	623.9	113.9
Goodwill disposed		(12.0)
Foreign currency, Goodwill	(30.1)	(70.7)
Ending balance, Goodwill	1,693.8	1,100.0
Retirement and Income Solutions
Changes in Goodwill
Beginning balance, Goodwill	57.4	57.4
Goodwill from acquisitions	618.5
Ending balance, Goodwill	675.9	57.4
Principal Global Investors
Changes in Goodwill
Beginning balance, Goodwill	307.3	247.3
Goodwill from acquisitions	6.5	65.0
Foreign currency, Goodwill	1.5	(5.0)
Other, Goodwill	2.2
Ending balance, Goodwill	317.5	307.3
Principal International
Changes in Goodwill
Beginning balance, Goodwill	676.6	707.5
Goodwill from acquisitions		46.8
Goodwill disposed		(12.0)
Foreign currency, Goodwill	(31.6)	(65.7)
Other, Goodwill	(2.2)
Ending balance, Goodwill	642.8	676.6
U.S. Insurance Solutions
Changes in Goodwill
Beginning balance, Goodwill	56.6	56.6
Ending balance, Goodwill	56.6	56.6
Corporate
Changes in Goodwill
Beginning balance, Goodwill	2.1
Goodwill from acquisitions	(1.1)	2.1
Ending balance, Goodwill	$ 1.0	$ 2.1

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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