Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues
Premiums and other considerations	$ 875.8	$ 703.0	$ 2,514.8	$ 2,134.9
Fees and other revenues	884.5	803.0	2,569.7	2,340.4
Net investment income (loss)	770.4	784.5	2,444.1	2,323.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(24.5)	(29.7)	105.0	(109.5)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	(7.3)	(11.9)	18.5	(81.2)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(14.6)	(9.3)	(82.5)	8.8
Net impairment losses on available-for-sale securities			(64.0)	(72.4)
Net realized capital gains (losses)	(46.4)	(50.9)	41.0	(181.9)
Total revenues	2,484.3	2,239.6	7,569.6	6,616.9
Expenses
Benefits, claims and settlement expenses	1,113.8	1,096.2	3,609.7	3,286.4
Dividends to policyholders	44.2	48.5	134.5	144.3
Operating expenses	932.5	774.6	2,647.7	2,372.1
Total expenses	2,090.5	1,919.3	6,391.9	5,802.8
Income (loss) before income taxes	393.8	320.3	1,177.7	814.1
Income taxes (benefits)	141.0	61.2	281.6	128.4
Net income (loss)	252.8	259.1	896.1	685.7
Net income (loss) attributable to noncontrolling interest	3.9	5.2	30.7	14.7
Net income (loss) attributable to Principal Financial Group, Inc.	248.9	253.9	865.4	671.0
Preferred stock dividends	8.2	8.2	24.7	24.7
Net income (loss) available to common stockholders	240.7	245.7	840.7	646.3
Net income (loss)	252.8	259.1	896.1	685.7
Other comprehensive income (loss)	(225.9)	(18.0)	190.1	(668.3)
Comprehensive income (loss)	26.9	241.1	1,086.2	17.4
Principal Financial Group, Inc. Parent Only
Revenues
Net investment income (loss)			0.4	0.4
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities				6.3
Net realized capital gains (losses)				6.3
Total revenues			0.4	6.7
Expenses
Operating expenses			106.8	105.2
Total expenses			106.8	105.2
Income (loss) before income taxes			(106.4)	(98.5)
Income taxes (benefits)			(42.7)	(39.4)
Equity in the net income (loss) of subsidiaries			929.1	730.1
Net income (loss)			865.4	671.0
Net income (loss) attributable to Principal Financial Group, Inc.			865.4	671.0
Preferred stock dividends			24.7	24.7
Net income (loss) available to common stockholders			840.7	646.3
Net income (loss)			865.4	671.0
Other comprehensive income (loss)			129.6	(683.9)
Comprehensive income (loss)			995.0	(12.9)
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			2,200.5	1,853.6
Fees and other revenues			1,407.5	1,272.3
Net investment income (loss)			1,719.4	1,775.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			674.1	(630.7)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities			27.7	(75.4)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(84.5)	11.4
Net impairment losses on available-for-sale securities			(56.8)	(64.0)
Net realized capital gains (losses)			617.3	(694.7)
Total revenues			5,944.7	4,206.9
Expenses
Benefits, claims and settlement expenses			3,083.8	2,828.8
Dividends to policyholders			134.5	144.3
Operating expenses			1,624.3	1,378.6
Total expenses			4,842.6	4,351.7
Income (loss) before income taxes			1,102.1	(144.8)
Income taxes (benefits)			260.6	(136.0)
Equity in the net income (loss) of subsidiaries			(125.0)	530.2
Net income (loss)			716.5	521.4
Net income (loss) attributable to Principal Financial Group, Inc.			716.5	521.4
Net income (loss) available to common stockholders			716.5	521.4
Net income (loss)			716.5	521.4
Other comprehensive income (loss)			334.8	(438.6)
Comprehensive income (loss)			1,051.3	82.8
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			314.3	281.3
Fees and other revenues			1,451.5	1,325.8
Net investment income (loss)			1,260.1	526.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(569.1)	514.8
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities			(9.2)	(5.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			2.0	(2.6)
Net impairment losses on available-for-sale securities			(7.2)	(8.4)
Net realized capital gains (losses)			(576.3)	506.4
Total revenues			2,449.6	2,640.0
Expenses
Benefits, claims and settlement expenses			534.5	466.7
Operating expenses			1,156.4	1,113.2
Total expenses			1,690.9	1,579.9
Income (loss) before income taxes			758.7	1,060.1
Income taxes (benefits)			65.3	304.0
Equity in the net income (loss) of subsidiaries			266.4	(11.2)
Net income (loss)			959.8	744.9
Net income (loss) attributable to noncontrolling interest			30.7	14.8
Net income (loss) attributable to Principal Financial Group, Inc.			929.1	730.1
Net income (loss) available to common stockholders			929.1	730.1
Net income (loss)			959.8	744.9
Other comprehensive income (loss)			275.7	(225.6)
Comprehensive income (loss)			1,235.5	519.3
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(289.3)	(257.7)
Net investment income (loss)			(535.8)	20.9
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities				0.1
Net realized capital gains (losses)				0.1
Total revenues			(825.1)	(236.7)
Expenses
Benefits, claims and settlement expenses			(8.6)	(9.1)
Operating expenses			(239.8)	(224.9)
Total expenses			(248.4)	(234.0)
Income (loss) before income taxes			(576.7)	(2.7)
Income taxes (benefits)			(1.6)	(0.2)
Equity in the net income (loss) of subsidiaries			(1,070.5)	(1,249.1)
Net income (loss)			(1,645.6)	(1,251.6)
Net income (loss) attributable to noncontrolling interest				(0.1)
Net income (loss) attributable to Principal Financial Group, Inc.			(1,645.6)	(1,251.5)
Net income (loss) available to common stockholders			(1,645.6)	(1,251.5)
Net income (loss)			(1,645.6)	(1,251.6)
Other comprehensive income (loss)			(550.0)	679.8
Comprehensive income (loss)			$ (2,195.6)	$ (571.8)