Consolidated Statements of Operations - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Premiums and other considerations	$ 1,265.8	$ 1,452.7	$ 2,261.0	$ 2,700.7
Fees and other revenues	1,012.6	955.1	2,023.9	1,895.7
Net investment income (loss)	889.1	866.4	1,791.3	1,743.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	76.4	(81.7)	61.2	(69.5)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	(8.2)	(2.4)	(6.9)	(29.7)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(0.8)	(11.8)	(12.0)	(13.3)
Net impairment (losses) recoveries on available-for-sale securities	(9.0)	(14.2)	(18.9)	(43.0)
Net realized capital gains (losses)	67.4	(95.9)	42.3	(112.5)
Total revenues	3,234.9	3,178.3	6,118.5	6,227.7
Expenses
Benefits, claims and settlement expenses	1,699.2	1,858.8	3,110.3	3,516.1
Dividends to policyholders	30.2	25.2	60.7	60.1
Operating expenses	990.1	928.7	1,975.1	1,871.9
Total expenses	2,719.5	2,812.7	5,146.1	5,448.1
Income (loss) before income taxes	515.4	365.6	972.4	779.6
Income taxes (benefits)	55.9	50.8	110.4	111.2
Net income (loss)	459.5	314.8	862.0	668.4
Net income (loss) attributable to noncontrolling interest	2.9	5.3	8.3	10.0
Net income (loss) attributable to Principal Financial Group, Inc.	$ 456.6	$ 309.5	$ 853.7	$ 658.4
Earnings per common share
Basic earnings per common share (in dollars per share)	$ 1.59	$ 1.07	$ 2.97	$ 2.28
Diluted earnings per common share (in dollars per share)	1.58	1.06	2.93	2.25
Dividends declared per common share (in dollars per share)	$ 0.52	$ 0.46	$ 1.03	$ 0.91