Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, 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
Net income (loss)	218.9	208.8
Other comprehensive income (loss)	230.9	259.3
Comprehensive income (loss)	449.8	468.1
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues	0.1
Net investment income (loss)	1.0	10.8
Total revenues	1.1	10.8
Expenses
Operating expenses	30.0	29.2
Total expenses	30.0	29.2
Income (loss) before income taxes	(28.9)	(18.4)
Income taxes (benefits)	(11.2)	(7.0)
Equity in the net income (loss) of subsidiaries	227.4	201.6
Net income (loss)	209.7	190.2
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
Net income (loss)	209.7	190.2
Other comprehensive income (loss)	186.3	279.0
Comprehensive income (loss)	396.0	469.2
Principal Life Insurance Company Only
Revenues
Premiums and other considerations	583.4	719.0
Fees and other revenues	343.8	397.8
Net investment income (loss)	626.8	643.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(350.5)	(25.9)
Total other-than-temporary impairment losses on available-for-sale securities	(33.0)	(11.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	4.5	(39.2)
Net impairment losses on available-for-sale securities	(28.5)	(51.0)
Net realized capital gains (losses)	(379.0)	(76.9)
Total revenues	1,175.0	1,683.7
Expenses
Benefits, claims and settlement expenses	1,034.5	1,052.6
Dividends to policyholders	50.3	53.6
Operating expenses	282.0	467.3
Total expenses	1,366.8	1,573.5
Income (loss) before income taxes	(191.8)	110.2
Income taxes (benefits)	(84.9)	24.6
Equity in the net income (loss) of subsidiaries	275.1	78.1
Net income (loss)	168.2	163.7
Net income (loss) attributable to Principal Financial Group, Inc.	168.2	163.7
Net income (loss) available to common stockholders	168.2	163.7
Net income (loss)	168.2	163.7
Other comprehensive income (loss)	141.5	229.8
Comprehensive income (loss)	309.7	393.5
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations	96.4	78.1
Fees and other revenues	329.7	300.1
Net investment income (loss)	195.4	183.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	389.3	21.9
Total other-than-temporary impairment losses on available-for-sale securities	(0.7)	(2.2)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	0.4	0.8
Net impairment losses on available-for-sale securities	(0.3)	(1.4)
Net realized capital gains (losses)	389.0	20.5
Total revenues	1,010.5	582.2
Expenses
Benefits, claims and settlement expenses	181.2	139.7
Operating expenses	309.9	286.5
Total expenses	491.1	426.2
Income (loss) before income taxes	519.4	156.0
Income taxes (benefits)	154.5	35.1
Equity in the net income (loss) of subsidiaries	(128.3)	99.3
Net income (loss)	236.6	220.2
Net income (loss) attributable to noncontrolling interest	9.2	18.6
Net income (loss) attributable to Principal Financial Group, Inc.	227.4	201.6
Net income (loss) available to common stockholders	227.4	201.6
Net income (loss)	236.6	220.2
Other comprehensive income (loss)	96.9	48.8
Comprehensive income (loss)	333.5	269.0
Eliminations, Notes Guarantor
Revenues
Fees and other revenues	(75.6)	(74.9)
Net investment income (loss)	1.6	21.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(16.7)	(1.6)
Net realized capital gains (losses)	(16.7)	(1.6)
Total revenues	(90.7)	(54.8)
Expenses
Benefits, claims and settlement expenses	(3.2)	(3.4)
Operating expenses	(65.9)	(65.1)
Total expenses	(69.1)	(68.5)
Income (loss) before income taxes	(21.6)	13.7
Income taxes (benefits)	(0.2)
Equity in the net income (loss) of subsidiaries	(374.2)	(379.0)
Net income (loss)	(395.6)	(365.3)
Net income (loss) attributable to Principal Financial Group, Inc.	(395.6)	(365.3)
Net income (loss) available to common stockholders	(395.6)	(365.3)
Net income (loss)	(395.6)	(365.3)
Other comprehensive income (loss)	(193.8)	(298.3)
Comprehensive income (loss)	$ (589.4)	$ (663.6)