Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues
Premiums and other considerations	$ 703.0	$ 1,158.2	$ 2,134.9	$ 2,519.3
Fees and other revenues	803.0	675.0	2,340.4	1,909.1
Net investment income (loss)	784.5	783.8	2,323.5	2,409.6
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(29.7)	122.1	(109.5)	176.4
Total other-than-temporary impairment losses on available-for-sale securities	(11.9)	(43.6)	(81.2)	(126.4)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(9.3)	9.2	8.8	31.2
Net impairment losses on available-for-sale securities			(72.4)	(95.2)
Net realized capital gains (losses)	(50.9)	87.7	(181.9)	81.2
Total revenues	2,239.6	2,704.7	6,616.9	6,919.2
Expenses
Benefits, claims and settlement expenses	1,096.2	1,647.0	3,286.4	3,969.5
Dividends to policyholders	48.5	49.7	144.3	149.5
Operating expenses	774.6	816.4	2,372.1	2,101.1
Total expenses	1,919.3	2,513.1	5,802.8	6,220.1
Income (loss) before income taxes	320.3	191.6	814.1	699.1
Income taxes (benefits)	61.2	(7.2)	128.4	100.4
Net income (loss)	259.1	198.8	685.7	598.7
Net income (loss) attributable to noncontrolling interest	5.2	3.4	14.7	15.3
Net income (loss) attributable to Principal Financial Group, Inc.	253.9	195.4	671.0	583.4
Preferred stock dividends	8.2	8.2	24.7	24.7
Net income (loss) available to common stockholders	245.7	187.2	646.3	558.7
Net income (loss)	259.1	198.8	685.7	598.7
Other comprehensive income (loss)	(18.0)	327.9	(668.3)	618.1
Comprehensive income (loss)	241.1	526.7	17.4	1,216.8
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues				0.3
Net investment income (loss)			0.4	2.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			6.3
Net realized capital gains (losses)			6.3
Total revenues			6.7	3.0
Expenses
Operating expenses			105.2	90.8
Total expenses			105.2	90.8
Income (loss) before income taxes			(98.5)	(87.8)
Income taxes (benefits)			(39.4)	(34.4)
Equity in the net income (loss) of subsidiaries			730.1	636.8
Net income (loss)			671.0	583.4
Net income (loss) attributable to Principal Financial Group, Inc.			671.0	583.4
Preferred stock dividends			24.7	24.7
Net income (loss) available to common stockholders			646.3	558.7
Net income (loss)			671.0	583.4
Other comprehensive income (loss)			(683.9)	564.6
Comprehensive income (loss)			(12.9)	1,148.0
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			1,853.6	2,265.7
Fees and other revenues			1,272.3	1,115.0
Net investment income (loss)			1,775.7	1,869.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(630.7)	(296.9)
Total other-than-temporary impairment losses on available-for-sale securities			(75.4)	(111.5)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			11.4	27.1
Net impairment losses on available-for-sale securities			(64.0)	(84.4)
Net realized capital gains (losses)			(694.7)	(381.3)
Total revenues			4,206.9	4,869.2
Expenses
Benefits, claims and settlement expenses			2,828.8	3,542.3
Dividends to policyholders			144.3	149.5
Operating expenses			1,378.6	1,286.3
Total expenses			4,351.7	4,978.1
Income (loss) before income taxes			(144.8)	(108.9)
Income taxes (benefits)			(136.0)	(126.4)
Equity in the net income (loss) of subsidiaries			530.2	438.6
Net income (loss)			521.4	456.1
Net income (loss) attributable to Principal Financial Group, Inc.			521.4	456.1
Net income (loss) available to common stockholders			521.4	456.1
Net income (loss)			521.4	456.1
Other comprehensive income (loss)			(438.6)	546.2
Comprehensive income (loss)			82.8	1,002.3
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			281.3	253.6
Fees and other revenues			1,325.8	1,018.9
Net investment income (loss)			526.5	521.9
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			514.8	496.8
Total other-than-temporary impairment losses on available-for-sale securities			(5.8)	(14.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(2.6)	4.1
Net impairment losses on available-for-sale securities			(8.4)	(10.7)
Net realized capital gains (losses)			506.4	486.1
Total revenues			2,640.0	2,280.5
Expenses
Benefits, claims and settlement expenses			466.7	436.7
Operating expenses			1,113.2	920.2
Total expenses			1,579.9	1,356.9
Income (loss) before income taxes			1,060.1	923.6
Income taxes (benefits)			304.0	261.7
Equity in the net income (loss) of subsidiaries			(11.2)	(9.7)
Net income (loss)			744.9	652.2
Net income (loss) attributable to noncontrolling interest			14.8	15.4
Net income (loss) attributable to Principal Financial Group, Inc.			730.1	636.8
Net income (loss) available to common stockholders			730.1	636.8
Net income (loss)			744.9	652.2
Other comprehensive income (loss)			(225.6)	104.7
Comprehensive income (loss)			519.3	756.9
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(257.7)	(225.1)
Net investment income (loss)			20.9	15.2
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			0.1	(23.5)
Total other-than-temporary impairment losses on available-for-sale securities				(0.1)
Net impairment losses on available-for-sale securities				(0.1)
Net realized capital gains (losses)			0.1	(23.6)
Total revenues			(236.7)	(233.5)
Expenses
Benefits, claims and settlement expenses			(9.1)	(9.5)
Operating expenses			(224.9)	(196.2)
Total expenses			(234.0)	(205.7)
Income (loss) before income taxes			(2.7)	(27.8)
Income taxes (benefits)			(0.2)	(0.5)
Equity in the net income (loss) of subsidiaries			(1,249.1)	(1,065.7)
Net income (loss)			(1,251.6)	(1,093.0)
Net income (loss) attributable to noncontrolling interest			(0.1)	(0.1)
Net income (loss) attributable to Principal Financial Group, Inc.			(1,251.5)	(1,092.9)
Net income (loss) available to common stockholders			(1,251.5)	(1,092.9)
Net income (loss)			(1,251.6)	(1,093.0)
Other comprehensive income (loss)			679.8	(597.4)
Comprehensive income (loss)			$ (571.8)	$ (1,690.4)