Condensed Consolidating Financial Information (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues
Premiums and other considerations	$ 1,682.4	$ 835.4	$ 2,598.8	$ 1,639.0
Fees and other revenues	901.5	855.5	1,852.3	1,685.2
Net investment income (loss)	789.9	829.0	1,513.8	1,673.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(108.6)	109.7	(34.9)	129.5
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	(0.6)	14.9	13.4	25.8
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(5.4)	(37.8)	(26.9)	(67.9)
Net impairment (losses) recoveries on available-for-sale securities	(6.0)	(22.9)	(13.5)	(42.1)
Net realized capital gains (losses)	(114.6)	86.8	(48.4)	87.4
Total revenues	3,259.2	2,606.7	5,916.5	5,085.3
Expenses
Benefits, claims and settlement expenses	2,054.6	1,268.4	3,290.9	2,495.9
Dividends to policyholders	41.1	44.6	82.8	90.3
Operating expenses	869.0	886.2	1,790.2	1,715.2
Total expenses	2,964.7	2,199.2	5,163.9	4,301.4
Income (loss) before income taxes	294.5	407.5	752.6	783.9
Income taxes (benefits)	29.6	88.3	58.6	140.6
Net income (loss)	264.9	319.2	694.0	643.3
Net income (loss) attributable to noncontrolling interest	7.3	4.6	14.0	26.8
Net income (loss) attributable to Principal Financial Group, Inc.	257.6	314.6	680.0	616.5
Preferred stock dividends	8.3	8.3	16.5	16.5
Excess of redemption value over carrying value of preferred shares redeemed	8.2		8.2
Net income (loss) available to common stockholders	241.1	306.3	655.3	600.0
Net income (loss)	264.9	319.2	694.0	643.3
Other comprehensive income (loss)	(349.6)	239.4	(371.8)	416.0
Comprehensive income (loss)	$ (84.7)	$ 558.6	322.2	1,059.3
Principal Financial Group, Inc. Parent Only
Revenues
Net investment income (loss)			0.8	0.1
Total revenues			0.8	0.1
Expenses
Operating expenses			82.4	71.7
Total expenses			82.4	71.7
Income (loss) before income taxes			(81.6)	(71.6)
Income taxes (benefits)			(33.9)	(28.8)
Equity in the net income (loss) of subsidiaries			727.7	659.3
Net income (loss)			680.0	616.5
Net income (loss) attributable to Principal Financial Group, Inc.			680.0	616.5
Preferred stock dividends			16.5	16.5
Excess of redemption value over carrying value of preferred shares redeemed			8.2
Net income (loss) available to common stockholders			655.3	600.0
Net income (loss)			680.0	616.5
Other comprehensive income (loss)			(436.8)	345.6
Comprehensive income (loss)			243.2	962.1
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			2,431.1	1,406.5
Fees and other revenues			1,035.5	926.9
Net investment income (loss)			1,074.2	1,164.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(4.9)	455.9
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities			13.5	31.5
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(26.9)	(68.0)
Net impairment (losses) recoveries on available-for-sale securities			(13.4)	(36.5)
Net realized capital gains (losses)			(18.3)	419.4
Total revenues			4,522.5	3,917.3
Expenses
Benefits, claims and settlement expenses			2,983.9	2,110.8
Dividends to policyholders			82.8	90.3
Operating expenses			1,078.3	1,048.2
Total expenses			4,145.0	3,249.3
Income (loss) before income taxes			377.5	668.0
Income taxes (benefits)			83.8	149.8
Equity in the net income (loss) of subsidiaries			147.8	(51.6)
Net income (loss)			441.5	466.6
Net income (loss) attributable to Principal Financial Group, Inc.			441.5	466.6
Net income (loss) available to common stockholders			441.5	466.6
Net income (loss)			441.5	466.6
Other comprehensive income (loss)			(203.0)	395.0
Comprehensive income (loss)			238.5	861.6
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			167.7	232.5
Fees and other revenues			1,022.5	953.1
Net investment income (loss)			707.4	803.9
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(30.0)	(326.4)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities			(0.1)	(5.7)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income				0.1
Net impairment (losses) recoveries on available-for-sale securities			(0.1)	(5.6)
Net realized capital gains (losses)			(30.1)	(332.0)
Total revenues			1,867.5	1,657.5
Expenses
Benefits, claims and settlement expenses			312.8	390.7
Operating expenses			799.4	755.2
Total expenses			1,112.2	1,145.9
Income (loss) before income taxes			755.3	511.6
Income taxes (benefits)			9.5	20.5
Equity in the net income (loss) of subsidiaries			(7.6)	195.0
Net income (loss)			738.2	686.1
Net income (loss) attributable to noncontrolling interest			14.0	26.8
Net income (loss) attributable to Principal Financial Group, Inc.			724.2	659.3
Net income (loss) available to common stockholders			724.2	659.3
Net income (loss)			738.2	686.1
Other comprehensive income (loss)			(369.5)	517.4
Comprehensive income (loss)			368.7	1,203.5
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(205.7)	(194.8)
Net investment income (loss)			(268.6)	(294.8)
Total revenues			(474.3)	(489.6)
Expenses
Benefits, claims and settlement expenses			(5.8)	(5.6)
Operating expenses			(169.9)	(159.9)
Total expenses			(175.7)	(165.5)
Income (loss) before income taxes			(298.6)	(324.1)
Income taxes (benefits)			(0.8)	(0.9)
Equity in the net income (loss) of subsidiaries			(867.9)	(802.7)
Net income (loss)			(1,165.7)	(1,125.9)
Net income (loss) attributable to Principal Financial Group, Inc.			(1,165.7)	(1,125.9)
Net income (loss) available to common stockholders			(1,165.7)	(1,125.9)
Net income (loss)			(1,165.7)	(1,125.9)
Other comprehensive income (loss)			637.5	(842.0)
Comprehensive income (loss)			$ (528.2)	$ (1,967.9)