Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenues
Premiums and other considerations	$ 916.4	$ 803.6
Fees and other revenues	950.8	829.7
Net investment income (loss)	723.9	844.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	73.7	19.8
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	14.0	10.9
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(21.5)	(30.1)
Net impairment (losses) recoveries on available-for-sale securities	(7.5)	(19.2)
Net realized capital gains (losses)	66.2	0.6
Total revenues	2,657.3	2,478.6
Expenses
Benefits, claims and settlement expenses	1,236.3	1,227.5
Dividends to policyholders	41.7	45.7
Operating expenses	921.2	829.0
Total expenses	2,199.2	2,102.2
Income (loss) before income taxes	458.1	376.4
Income taxes (benefits)	29.0	52.3
Net income (loss)	429.1	324.1
Net income (loss) attributable to noncontrolling interest	6.7	22.2
Net income (loss) attributable to Principal Financial Group, Inc.	422.4	301.9
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	414.2	293.7
Net income (loss)	429.1	324.1
Other comprehensive income (loss)	(22.2)	176.6
Comprehensive income (loss)	406.9	500.7
Principal Financial Group, Inc. Parent Only
Revenues
Net investment income (loss)	0.3	0.1
Total revenues	0.3	0.1
Expenses
Operating expenses	38.6	35.6
Total expenses	38.6	35.6
Income (loss) before income taxes	(38.3)	(35.5)
Income taxes (benefits)	(16.3)	(14.2)
Equity in the net income (loss) of subsidiaries	444.4	323.2
Net income (loss)	422.4	301.9
Net income (loss) attributable to Principal Financial Group, Inc.	422.4	301.9
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	414.2	293.7
Net income (loss)	422.4	301.9
Other comprehensive income (loss)	(85.7)	111.1
Comprehensive income (loss)	336.7	413.0
Principal Life Insurance Company Only
Revenues
Premiums and other considerations	850.6	705.7
Fees and other revenues	549.1	458.7
Net investment income (loss)	530.1	576.3
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	413.3	244.3
Net other-than-temporary impairment (losses) recoveries on available-for-sale securities	14.0	10.9
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(21.2)	(29.3)
Net impairment (losses) recoveries on available-for-sale securities	(7.2)	(18.4)
Net realized capital gains (losses)	406.1	225.9
Total revenues	2,335.9	1,966.6
Expenses
Benefits, claims and settlement expenses	1,118.2	1,057.9
Dividends to policyholders	41.7	45.7
Operating expenses	578.7	499.8
Total expenses	1,738.6	1,603.4
Income (loss) before income taxes	597.3	363.2
Income taxes (benefits)	206.3	74.3
Equity in the net income (loss) of subsidiaries	(149.4)	(53.6)
Net income (loss)	241.6	235.3
Net income (loss) attributable to Principal Financial Group, Inc.	241.6	235.3
Net income (loss) available to common stockholders	241.6	235.3
Net income (loss)	241.6	235.3
Other comprehensive income (loss)	83.4	188.3
Comprehensive income (loss)	325.0	423.6
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations	65.8	97.9
Fees and other revenues	508.3	471.3
Net investment income (loss)	269.4	339.1
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(339.6)	(224.5)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(0.3)	(0.8)
Net impairment (losses) recoveries on available-for-sale securities	(0.3)	(0.8)
Net realized capital gains (losses)	(339.9)	(225.3)
Total revenues	503.6	683.0
Expenses
Benefits, claims and settlement expenses	121.0	172.4
Operating expenses	388.4	374.8
Total expenses	509.4	547.2
Income (loss) before income taxes	(5.8)	135.8
Income taxes (benefits)	(160.7)	(7.7)
Equity in the net income (loss) of subsidiaries	294.4	201.9
Net income (loss)	449.3	345.4
Net income (loss) attributable to noncontrolling interest	6.7	22.2
Net income (loss) attributable to Principal Financial Group, Inc.	442.6	323.2
Net income (loss) available to common stockholders	442.6	323.2
Net income (loss)	449.3	345.4
Other comprehensive income (loss)	16.5	255.9
Comprehensive income (loss)	465.8	601.3
Eliminations, Notes Guarantor
Revenues
Fees and other revenues	(106.6)	(100.3)
Net investment income (loss)	(75.9)	(70.8)
Total revenues	(182.5)	(171.1)
Expenses
Benefits, claims and settlement expenses	(2.9)	(2.8)
Operating expenses	(84.5)	(81.2)
Total expenses	(87.4)	(84.0)
Income (loss) before income taxes	(95.1)	(87.1)
Income taxes (benefits)	(0.3)	(0.1)
Equity in the net income (loss) of subsidiaries	(589.4)	(471.5)
Net income (loss)	(684.2)	(558.5)
Net income (loss) attributable to Principal Financial Group, Inc.	(684.2)	(558.5)
Net income (loss) available to common stockholders	(684.2)	(558.5)
Net income (loss)	(684.2)	(558.5)
Other comprehensive income (loss)	(36.4)	(378.7)
Comprehensive income (loss)	$ (720.6)	$ (937.2)