Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Premiums and other considerations	$ 6,217.4	$ 5,299.1	$ 5,310.3
Fees and other revenues	3,892.3	3,627.4	3,653.1
Net investment income (loss)	3,459.3	3,296.5	3,052.1
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	606.0	269.5	(20.9)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	(28.7)	(98.8)	(0.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(53.1)	0.4	(29.4)
Net impairment (losses) recoveries on available-for-sale securities	(81.8)	(98.4)	(30.2)
Net realized capital gains (losses)	524.2	171.1	(51.1)
Total revenues	14,093.2	12,394.1	11,964.4
Expenses
Benefits, claims and settlement expenses	7,822.6	6,913.2	6,697.7
Dividends to policyholders	124.6	156.6	163.5
Operating expenses	3,893.8	3,732.6	3,672.4
Total expenses	11,841.0	10,802.4	10,533.6
Income (loss) before income taxes	2,252.2	1,591.7	1,430.8
Income taxes (benefits)	(72.3)	229.9	177.6
Net income (loss)	2,324.5	1,361.8	1,253.2
Net income (loss) attributable to noncontrolling interest	14.1	45.3	19.2
Net income (loss) attributable to Principal Financial Group, Inc.	2,310.4	1,316.5	1,234.0
Preferred stock dividends			16.5
Excess of redemption value over carrying value of preferred shares redeemed			8.2
Net income (loss) available to common stockholders	$ 2,310.4	$ 1,316.5	$ 1,209.3
Earnings per common share
Basic earnings per common share (in dollars per share)	$ 8.00	$ 4.55	$ 4.11
Diluted earnings per common share (in dollars per share)	7.88	4.50	4.06
Dividends declared per common share (in dollars per share)	$ 1.87	$ 1.61	$ 1.50