Condensed Consolidating Financial Information (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues
Premiums and other considerations	$ 1,557.1	$ 875.8	$ 4,155.9	$ 2,514.8
Fees and other revenues	891.9	884.5	2,744.2	2,569.7
Net investment income (loss)	753.5	770.4	2,267.3	2,444.1
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	46.0	(24.5)	11.1	105.0
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	(6.5)	(7.3)	6.9	18.5
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(1.1)	(14.6)	(28.0)	(82.5)
Net impairment (losses) recoveries on available-for-sale securities	(7.6)	(21.9)	(21.1)	(64.0)
Net realized capital gains (losses)	38.4	(46.4)	(10.0)	41.0
Total revenues	3,240.9	2,484.3	9,157.4	7,569.6
Expenses
Benefits, claims and settlement expenses	1,869.6	1,113.8	5,160.5	3,609.7
Dividends to policyholders	40.7	44.2	123.5	134.5
Operating expenses	961.4	932.5	2,751.6	2,647.7
Total expenses	2,871.7	2,090.5	8,035.6	6,391.9
Income (loss) before income taxes	369.2	393.8	1,121.8	1,177.7
Income taxes (benefits)	68.3	141.0	126.9	281.6
Net income (loss)	300.9	252.8	994.9	896.1
Net income (loss) attributable to noncontrolling interest	0.5	3.9	14.5	30.7
Net income (loss) attributable to Principal Financial Group, Inc.	300.4	248.9	980.4	865.4
Preferred stock dividends		8.2	16.5	24.7
Excess of redemption value over carrying value of preferred shares redeemed			8.2
Net income (loss) available to common stockholders	300.4	240.7	955.7	840.7
Net income (loss)	300.9	252.8	994.9	896.1
Other comprehensive income (loss)	(211.7)	(225.9)	(583.5)	190.1
Comprehensive income (loss)	$ 89.2	$ 26.9	411.4	1,086.2
Principal Financial Group, Inc. Parent Only
Revenues
Net investment income (loss)			1.3	0.4
Total revenues			1.3	0.4
Expenses
Operating expenses			128.5	106.8
Total expenses			128.5	106.8
Income (loss) before income taxes			(127.2)	(106.4)
Income taxes (benefits)			(52.5)	(42.7)
Equity in the net income (loss) of subsidiaries			1,055.1	929.1
Net income (loss)			980.4	865.4
Net income (loss) attributable to Principal Financial Group, Inc.			980.4	865.4
Preferred stock dividends			16.5	24.7
Excess of redemption value over carrying value of preferred shares redeemed			8.2
Net income (loss) available to common stockholders			955.7	840.7
Net income (loss)			980.4	865.4
Other comprehensive income (loss)			(633.8)	129.6
Comprehensive income (loss)			346.6	995.0
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			3,885.3	2,200.5
Fees and other revenues			1,522.0	1,407.5
Net investment income (loss)			1,606.8	1,719.4
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			50.4	674.1
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities			6.9	27.7
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(27.9)	(84.5)
Net impairment (losses) recoveries on available-for-sale securities			(21.0)	(56.8)
Net realized capital gains (losses)			29.4	617.3
Total revenues			7,043.5	5,944.7
Expenses
Benefits, claims and settlement expenses			4,685.3	3,083.8
Dividends to policyholders			123.5	134.5
Operating expenses			1,658.7	1,624.3
Total expenses			6,467.5	4,842.6
Income (loss) before income taxes			576.0	1,102.1
Income taxes (benefits)			106.0	260.6
Equity in the net income (loss) of subsidiaries			262.6	(125.0)
Net income (loss)			732.6	716.5
Net income (loss) attributable to Principal Financial Group, Inc.			732.6	716.5
Net income (loss) available to common stockholders			732.6	716.5
Net income (loss)			732.6	716.5
Other comprehensive income (loss)			(181.1)	334.8
Comprehensive income (loss)			551.5	1,051.3
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			270.6	314.3
Fees and other revenues			1,523.9	1,451.5
Net investment income (loss)			1,212.0	1,260.1
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(39.3)	(569.1)
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities				(9.2)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(0.1)	2.0
Net impairment (losses) recoveries on available-for-sale securities			(0.1)	(7.2)
Net realized capital gains (losses)			(39.4)	(576.3)
Total revenues			2,967.1	2,449.6
Expenses
Benefits, claims and settlement expenses			483.8	534.5
Operating expenses			1,216.9	1,156.4
Total expenses			1,700.7	1,690.9
Income (loss) before income taxes			1,266.4	758.7
Income taxes (benefits)			74.4	65.3
Equity in the net income (loss) of subsidiaries			(127.5)	266.4
Net income (loss)			1,064.5	959.8
Net income (loss) attributable to noncontrolling interest			14.5	30.7
Net income (loss) attributable to Principal Financial Group, Inc.			1,050.0	929.1
Net income (loss) available to common stockholders			1,050.0	929.1
Net income (loss)			1,064.5	959.8
Other comprehensive income (loss)			(606.7)	275.7
Comprehensive income (loss)			457.8	1,235.5
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(301.7)	(289.3)
Net investment income (loss)			(552.8)	(535.8)
Total revenues			(854.5)	(825.1)
Expenses
Benefits, claims and settlement expenses			(8.6)	(8.6)
Operating expenses			(252.5)	(239.8)
Total expenses			(261.1)	(248.4)
Income (loss) before income taxes			(593.4)	(576.7)
Income taxes (benefits)			(1.0)	(1.6)
Equity in the net income (loss) of subsidiaries			(1,190.2)	(1,070.5)
Net income (loss)			(1,782.6)	(1,645.6)
Net income (loss) attributable to Principal Financial Group, Inc.			(1,782.6)	(1,645.6)
Net income (loss) available to common stockholders			(1,782.6)	(1,645.6)
Net income (loss)			(1,782.6)	(1,645.6)
Other comprehensive income (loss)			838.1	(550.0)
Comprehensive income (loss)			$ (944.5)	$ (2,195.6)