Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Consolidated Statements of Comprehensive Income
Net income (loss)	$ 459.5	$ 314.8	$ 862.0	$ 668.4
Other comprehensive income (loss), net:
Net unrealized gains (losses) on available-for-sale securities	(466.1)	335.1	(1,271.6)	499.0
Noncredit component of impairment losses on fixed maturities, available-for-sale	0.8	7.0	10.1	7.7
Net unrealized gains (losses) on derivative instruments	20.3	(6.0)	5.9	(18.2)
Foreign currency translation adjustment	(236.1)	(1.7)	(170.3)	62.7
Net unrecognized postretirement benefit obligation	8.8	4.3	17.5	8.6
Other comprehensive income (loss)	(672.3)	338.7	(1,408.4)	559.8
Comprehensive income (loss)	(212.8)	653.5	(546.4)	1,228.2
Comprehensive income (loss) attributable to noncontrolling interest	(0.8)	5.0	5.5	10.7
Comprehensive income (loss) attributable to Principal Financial Group, Inc.	$ (212.0)	$ 648.5	$ (551.9)	$ 1,217.5