Condensed Consolidating Financial Information (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenues
Premiums and other considerations	$ 694.7	$ 679.8
Fees and other revenues	733.6	598.0
Net investment income (loss)	789.3	824.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(26.4)	22.1
Total other-than-temporary impairment losses on available-for-sale securities	(44.7)	(33.7)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	20.2	4.9
Net impairment losses on available-for-sale securities	(24.5)	(28.8)
Net realized capital gains (losses)	(50.9)	(6.7)
Total revenues	2,166.7	2,095.9
Expenses
Benefits, claims and settlement expenses	1,094.5	1,212.5
Dividends to policyholders	48.3	50.3
Operating expenses	795.7	555.1
Total expenses	1,938.5	1,817.9
Income (loss) before income taxes	228.2	278.0
Income taxes (benefits)	38.2	56.7
Net income (loss)	190.0	221.3
Net income (loss) attributable to noncontrolling interest	3.5	9.2
Net income (loss) attributable to Principal Financial Group, Inc.	186.5	212.1
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	178.3	203.9
Net income (loss)	190.0	221.3
Other comprehensive income (loss)	(20.4)	225.2
Comprehensive income (loss)	169.6	446.5
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues		0.1
Net investment income (loss)		1.0
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	6.3
Net realized capital gains (losses)	6.3
Total revenues	6.3	1.1
Expenses
Operating expenses	35.0	29.9
Total expenses	35.0	29.9
Income (loss) before income taxes	(28.7)	(28.8)
Income taxes (benefits)	(11.5)	(11.3)
Equity in the net income (loss) of subsidiaries	203.7	229.6
Net income (loss)	186.5	212.1
Net income (loss) attributable to Principal Financial Group, Inc.	186.5	212.1
Preferred stock dividends	8.2	8.2
Net income (loss) available to common stockholders	178.3	203.9
Net income (loss)	186.5	212.1
Other comprehensive income (loss)	(81.3)	180.6
Comprehensive income (loss)	105.2	392.7
Principal Financial Services, Inc. Only
Revenues
Net investment income (loss)	0.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	2.1
Net realized capital gains (losses)	2.1
Total revenues	2.8
Expenses
Operating expenses	8.2	0.4
Total expenses	8.2	0.4
Income (loss) before income taxes	(5.4)	(0.4)
Income taxes (benefits)	(1.0)	(1.7)
Equity in the net income (loss) of subsidiaries	208.1	228.3
Net income (loss)	203.7	229.6
Net income (loss) attributable to Principal Financial Group, Inc.	203.7	229.6
Net income (loss) available to common stockholders	203.7	229.6
Net income (loss)	203.7	229.6
Other comprehensive income (loss)	(21.9)	224.3
Comprehensive income (loss)	181.8	453.9
Principal Life Insurance Company and Other Subsidiaries Combined
Revenues
Premiums and other considerations	694.7	679.8
Fees and other revenues	733.7	598.2
Net investment income (loss)	788.5	823.5
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(34.8)	22.1
Total other-than-temporary impairment losses on available-for-sale securities	(44.7)	(33.7)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	20.2	4.9
Net impairment losses on available-for-sale securities	(24.5)	(28.8)
Net realized capital gains (losses)	(59.3)	(6.7)
Total revenues	2,157.6	2,094.8
Expenses
Benefits, claims and settlement expenses	1,094.5	1,212.5
Dividends to policyholders	48.3	50.3
Operating expenses	752.5	524.8
Total expenses	1,895.3	1,787.6
Income (loss) before income taxes	262.3	307.2
Income taxes (benefits)	50.7	69.7
Net income (loss)	211.6	237.5
Net income (loss) attributable to noncontrolling interest	3.5	9.2
Net income (loss) attributable to Principal Financial Group, Inc.	208.1	228.3
Net income (loss) available to common stockholders	208.1	228.3
Net income (loss)	211.6	237.5
Other comprehensive income (loss)	(21.0)	224.9
Comprehensive income (loss)	190.6	462.4
Eliminations, Shelf Registration Debt Guarantor
Revenues
Fees and other revenues	(0.1)	(0.3)
Net investment income (loss)	0.1	0.3
Expenses
Equity in the net income (loss) of subsidiaries	(411.8)	(457.9)
Net income (loss)	(411.8)	(457.9)
Net income (loss) attributable to Principal Financial Group, Inc.	(411.8)	(457.9)
Net income (loss) available to common stockholders	(411.8)	(457.9)
Net income (loss)	(411.8)	(457.9)
Other comprehensive income (loss)	103.8	(404.6)
Comprehensive income (loss)	$ (308.0)	$ (862.5)