Condensed Consolidating Financial Information (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues
Premiums and other considerations					$ 700.1	$ 1,158.2	$ 681.3	$ 679.8	$ 3,154.1	$ 3,219.4	$ 2,891.0
Fees and other revenues					717.6	675.0	636.1	598.0	3,222.2	2,626.7	2,526.7
Net investment income (loss)					845.3	783.8	801.0	824.8	3,138.4	3,254.9	3,375.3
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities					56.3	122.1	32.2	22.1	(109.2)	232.7	75.0
Total other-than-temporary impairment losses on available-for-sale securities					(9.5)	(43.6)	(49.1)	(33.7)	(91.5)	(135.9)	(147.6)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income					(13.9)	9.2	17.1	4.9	(24.5)	17.3	(49.7)
Net impairment losses on available-for-sale securities									(116.0)	(118.6)	(197.3)
Net realized capital gains (losses)					32.9	87.7	0.2	(6.7)	(225.2)	114.1	(122.3)
Total revenues	2,672.6	2,239.6	2,210.6	2,166.7	2,295.9	2,704.7	2,118.6	2,095.9	9,289.5	9,215.1	8,670.7
Expenses
Benefits, claims and settlement expenses					1,154.4	1,647.0	1,110.0	1,212.5	4,683.6	5,123.9	4,616.6
Dividends to policyholders					48.2	49.7	49.5	50.3	189.0	197.7	210.2
Operating expenses					832.4	816.4	729.6	555.1	3,292.9	2,933.5	2,971.1
Total expenses	2,362.7	1,919.3	1,945.0	1,938.5	2,035.0	2,513.1	1,889.1	1,817.9	8,165.5	8,255.1	7,797.9
Income (loss) before income taxes					260.9	191.6	229.5	278.0	1,124.0	960.0	872.8
Income taxes (benefits)					34.2	(7.2)	50.9	56.7	187.9	134.6	198.3
Net income (loss)	250.4	259.1	236.6	190.0	226.7	198.8	178.6	221.3	936.1	825.4	674.5
Net income (loss) attributable to noncontrolling interest					3.5	3.4	2.7	9.2	23.4	18.8	36.2
Net income (loss) attributable to Principal Financial Group, Inc.					223.2	195.4	175.9	212.1	912.7	806.6	638.3
Preferred stock dividends					8.3	8.2	8.3	8.2	33.0	33.0	33.0
Net income (loss) available to common stockholders	233.4	245.7	222.3	178.3	214.9	187.2	167.6	203.9	879.7	773.6	605.3
Net income (loss)	250.4	259.1	236.6	190.0	226.7	198.8	178.6	221.3	936.1	825.4	674.5
Other comprehensive income (loss)									(471.9)	370.1	(40.6)
Comprehensive income (loss)									464.2	1,195.5	633.9
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues										0.5	0.2
Net investment income (loss)									0.4	3.0	(12.0)
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									6.3	0.3
Net realized capital gains (losses)									6.3	0.3
Total revenues									6.7	3.8	(11.8)
Expenses
Operating expenses									140.5	170.2	116.0
Total expenses									140.5	170.2	116.0
Income (loss) before income taxes									(133.8)	(166.4)	(127.8)
Income taxes (benefits)									(54.0)	(67.6)	(50.4)
Equity in the net income (loss) of subsidiaries									992.5	905.4	715.7
Net income (loss)									912.7	806.6	638.3
Net income (loss) attributable to Principal Financial Group, Inc.									912.7	806.6	638.3
Preferred stock dividends									33.0	33.0	33.0
Net income (loss) available to common stockholders									879.7	773.6	605.3
Net income (loss)									912.7	806.6	638.3
Other comprehensive income (loss)									(450.1)	321.2	(34.5)
Comprehensive income (loss)									462.6	1,127.8	603.8
Principal Financial Services, Inc. Only
Revenues
Fees and other revenues									1.0
Net investment income (loss)									1.3	0.4	(3.2)
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									4.6	3.0	(0.1)
Net realized capital gains (losses)									4.6	3.0	(0.1)
Total revenues									6.9	3.4	(3.3)
Expenses
Operating expenses									9.0	9.3	1.7
Total expenses									9.0	9.3	1.7
Income (loss) before income taxes									(2.1)	(5.9)	(5.0)
Income taxes (benefits)									(2.9)	(6.9)	(9.9)
Equity in the net income (loss) of subsidiaries									991.7	904.4	710.8
Net income (loss)									992.5	905.4	715.7
Net income (loss) attributable to Principal Financial Group, Inc.									992.5	905.4	715.7
Net income (loss) available to common stockholders									992.5	905.4	715.7
Net income (loss)									992.5	905.4	715.7
Other comprehensive income (loss)									(476.4)	366.3	(44.0)
Comprehensive income (loss)									516.1	1,271.7	671.7
Principal Life Insurance Company and Other Subsidiaries Combined
Revenues
Premiums and other considerations									3,154.1	3,219.4	2,891.0
Fees and other revenues									3,250.2	2,627.3	2,529.5
Net investment income (loss)									3,136.5	3,250.8	3,387.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities									(120.1)	229.6	75.1
Total other-than-temporary impairment losses on available-for-sale securities									(91.5)	(135.9)	(147.6)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income									(24.5)	17.3	(49.7)
Net impairment losses on available-for-sale securities									(116.0)	(118.6)	(197.3)
Net realized capital gains (losses)									(236.1)	111.0	(122.2)
Total revenues									9,304.7	9,208.5	8,685.8
Expenses
Benefits, claims and settlement expenses									4,683.6	5,123.9	4,616.6
Dividends to policyholders									189.0	197.7	210.2
Operating expenses									3,172.2	2,754.6	2,853.4
Total expenses									8,044.8	8,076.2	7,680.2
Income (loss) before income taxes									1,259.9	1,132.3	1,005.6
Income taxes (benefits)									244.8	209.1	258.6
Net income (loss)									1,015.1	923.2	747.0
Net income (loss) attributable to noncontrolling interest									23.4	18.8	36.2
Net income (loss) attributable to Principal Financial Group, Inc.									991.7	904.4	710.8
Net income (loss) available to common stockholders									991.7	904.4	710.8
Net income (loss)									1,015.1	923.2	747.0
Other comprehensive income (loss)									(489.3)	353.7	(51.1)
Comprehensive income (loss)									525.8	1,276.9	695.9
Eliminations, Shelf Registration Debt Guarantor
Revenues
Fees and other revenues									(29.0)	(1.1)	(3.0)
Net investment income (loss)									0.2	0.7	3.0
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities										(0.2)
Net realized capital gains (losses)										(0.2)
Total revenues									(28.8)	(0.6)
Expenses
Operating expenses									(28.8)	(0.6)
Total expenses									(28.8)	(0.6)
Equity in the net income (loss) of subsidiaries									(1,984.2)	(1,809.8)	(1,426.5)
Net income (loss)									(1,984.2)	(1,809.8)	(1,426.5)
Net income (loss) attributable to Principal Financial Group, Inc.									(1,984.2)	(1,809.8)	(1,426.5)
Net income (loss) available to common stockholders									(1,984.2)	(1,809.8)	(1,426.5)
Net income (loss)									(1,984.2)	(1,809.8)	(1,426.5)
Other comprehensive income (loss)									943.9	(671.1)	89.0
Comprehensive income (loss)									$ (1,040.3)	$ (2,480.9)	$ (1,337.5)