Condensed Consolidating Financial Information (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
Premiums and other considerations									$ 2,891.0	$ 3,555.5	$ 3,750.6
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), excluding impairment losses on available-for-sale securities									75.0	48.7	54.9
Total other-than-temporary impairment losses on available-for-sale securities									(147.6)	(296.3)	(714.1)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income									(49.7)	56.1	260.9
Net impairment losses on available-for-sale securities									(197.3)	(240.2)	(453.2)
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
Benefits, claims and settlement expenses									4,454.1	5,338.4	5,334.5
Dividends to policyholders									210.2	219.9	242.2
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)	171.9	66.3	289.9	223.1	218.1	151.3	144.2	203.6	751.2	717.2	645.7
Net income (loss) attributable to noncontrolling interest									36.2	17.9	23.0
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), excluding impairment losses on available-for-sale securities										0.7	0.1
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)									715.0	699.3	622.7
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
Principal Life Insurance Company Only
Revenues
Premiums and other considerations									2,579.6	3,260.2	3,479.9
Fees and other revenues									1,605.1	1,444.0	1,351.7
Net investment income (loss)									2,578.8	2,800.9	2,931.0
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									442.8	160.2	(436.6)
Total other-than-temporary impairment losses on available-for-sale securities									(130.6)	(284.7)	(703.3)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income									(51.5)	51.6	256.8
Net impairment losses on available-for-sale securities									(182.1)	(233.1)	(446.5)
Net realized capital gains (losses)									260.7	(72.9)	(883.1)
Total revenues									7,024.2	7,432.2	6,879.5
Expenses
Benefits, claims and settlement expenses									3,850.5	4,834.9	5,007.6
Dividends to policyholders									210.2	219.9	242.2
Operating expenses									2,077.9	1,845.5	1,665.3
Total expenses									6,138.6	6,900.3	6,915.1
Income (loss) before income taxes									885.6	531.9	(35.6)
Income taxes (benefits)									297.7	119.1	(72.7)
Equity in the net income (loss) of subsidiaries									7.2	72.5	466.7
Net income (loss)									595.1	485.3	503.8
Net income (loss) attributable to Principal Financial Group, Inc.									595.1	485.3	503.8
Net income (loss) available to common stockholders									595.1	485.3	503.8
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations									311.4	295.3	270.7
Fees and other revenues									1,257.6	1,139.1	1,023.7
Net investment income (loss)									763.8	629.0	405.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									(388.7)	(111.9)	581.2
Total other-than-temporary impairment losses on available-for-sale securities									(17.0)	(11.6)	(10.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income									1.8	4.5	4.1
Net impairment losses on available-for-sale securities									(15.2)	(7.1)	(6.7)
Net realized capital gains (losses)									(403.9)	(119.0)	574.5
Total revenues									1,928.9	1,944.4	2,274.6
Expenses
Benefits, claims and settlement expenses									616.9	520.6	343.5
Operating expenses									1,116.6	1,034.6	997.2
Total expenses									1,733.5	1,555.2	1,340.7
Income (loss) before income taxes									195.4	389.2	933.9
Income taxes (benefits)									(11.1)	36.6	206.9
Equity in the net income (loss) of subsidiaries									622.3	416.2	(28.7)
Net income (loss)									828.8	768.8	698.3
Net income (loss) attributable to noncontrolling interest									36.4	18.1	23.2
Net income (loss) attributable to Principal Financial Group, Inc.									792.4	750.7	675.1
Net income (loss) available to common stockholders									792.4	750.7	675.1
Eliminations, Notes Guarantor
Revenues
Fees and other revenues									(297.8)	(285.1)	(279.4)
Net investment income (loss)									45.2	33.4	60.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									20.9	(0.3)	(89.8)
Net realized capital gains (losses)									20.9	(0.3)	(89.8)
Total revenues									(231.7)	(252.0)	(308.7)
Expenses
Benefits, claims and settlement expenses									(13.3)	(17.1)	(16.6)
Operating expenses									(252.8)	(238.1)	(226.7)
Total expenses									(266.1)	(255.2)	(243.3)
Income (loss) before income taxes									34.4	3.2	(65.4)
Income taxes (benefits)									0.2		0.6
Equity in the net income (loss) of subsidiaries									(1,421.9)	(1,239.4)	(1,113.1)
Net income (loss)									(1,387.7)	(1,236.2)	(1,179.1)
Net income (loss) attributable to noncontrolling interest									(0.2)	(0.2)	(0.2)
Net income (loss) attributable to Principal Financial Group, Inc.									(1,387.5)	(1,236.0)	(1,178.9)
Net income (loss) available to common stockholders									$ (1,387.5)	$ (1,236.0)	$ (1,178.9)