Consolidated Statements of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Revenues
Premiums and other considerations	$ 679.8	$ 797.1
Fees and other revenues	598.0	623.0
Net investment income (loss)	824.8	859.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	22.1	(5.6)
Total other-than-temporary impairment losses on available-for-sale securities	(33.7)	(14.0)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	4.9	(38.4)
Net impairment losses on available-for-sale securities	(28.8)	(52.4)
Net realized capital gains (losses)	(6.7)	(58.0)
Total revenues	2,095.9	2,221.9
Expenses
Benefits, claims and settlement expenses	1,212.5	1,188.9
Dividends to policyholders	50.3	53.6
Operating expenses	556.0	717.9
Total expenses	1,818.8	1,960.4
Income (loss) before income taxes	277.1	261.5
Income taxes (benefits)	58.2	52.7
Net income (loss)	218.9	208.8
Net income (loss) attributable to noncontrolling interest	9.2	18.6
Net income (loss) attributable to Principal Financial Group, Inc.	209.7	190.2
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	$ 201.5	$ 182.0
Earnings per common share
Basic earnings per common share (in dollars per share)	$ 0.67	$ 0.57
Diluted earnings per common share (in dollars per share)	$ 0.66	$ 0.56