Schedule II - Condensed Financial Information of Registrant (Parent Only) (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues
Fees and other revenues									$ 2,565.1	$ 2,298.1	$ 2,096.0
Net investment income (loss)									3,375.8	3,496.5	3,400.8
Net realized capital gains (losses)									(122.3)	(191.5)	(398.3)
Total revenues	2,059.0	2,088.8	2,342.0	2,219.8	2,372.5	2,288.5	2,233.6	2,264.0	8,709.6	9,158.6	8,849.1
Expenses
Operating expenses									3,057.7	2,759.0	2,526.6
Total expenses	1,865.4	1,950.6	1,969.7	1,936.3	2,108.8	2,125.0	2,075.8	2,007.7	7,722.0	8,317.3	8,103.3
Income (loss) before income taxes									987.6	841.3	745.8
Income taxes (benefits)									236.4	124.1	100.1
Net income (loss) attributable to Principal Financial Group, Inc.									715.0	699.3	622.7
Preferred stock dividends									33.0	33.0	33.0
Net income (loss) available to common stockholders	164.0	63.7	258.0	196.3	199.3	142.2	134.0	190.8	682.0	666.3	589.7
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues									0.2	0.1
Net investment income (loss)									(12.0)	33.2	3.6
Net realized capital gains (losses)										0.7	0.1
Total revenues									(11.8)	34.0	3.7
Expenses
Operating expenses									116.0	117.0	90.8
Total expenses									116.0	117.0	90.8
Income (loss) before income taxes									(127.8)	(83.0)	(87.1)
Income taxes (benefits)									(50.4)	(31.6)	(34.7)
Equity in the net income (loss) of subsidiaries									792.4	750.7	675.1
Net income (loss) attributable to Principal Financial Group, Inc.									715.0	699.3	622.7
Preferred stock dividends									33.0	33.0	33.0
Net income (loss) available to common stockholders									$ 682.0	$ 666.3	$ 589.7