Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Comprehensive Income
Net income (loss)	$ 2,324.5	$ 1,361.8	$ 1,253.2
Other comprehensive income (loss), net:
Net unrealized gains (losses) on available-for-sale securities	639.5	99.1	(470.7)
Noncredit component of impairment losses on fixed maturities, available-for-sale	31.2	(3.5)	19.1
Net unrealized gains (losses) on derivative instruments	(42.6)	15.5	19.2
Foreign currency translation adjustment	178.9	68.1	(471.6)
Net unrecognized postretirement benefit obligation	37.3	41.8	(39.1)
Other comprehensive income (loss)	844.3	221.0	(943.1)
Comprehensive income (loss)	3,168.8	1,582.8	310.1
Comprehensive income (loss) attributable to noncontrolling interest	17.7	49.7	(1.3)
Comprehensive income (loss) attributable to Principal Financial Group, Inc.	$ 3,151.1	$ 1,533.1	$ 311.4