Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues
Premiums and other considerations	$ 1,158.2	$ 672.7	$ 2,519.3	$ 2,221.7
Fees and other revenues	675.0	636.4	1,909.1	1,892.6
Net investment income (loss)	783.8	815.2	2,409.6	2,548.6
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	122.1	16.9	176.4	99.6
Total other-than-temporary impairment losses on available-for-sale securities	(43.6)	(12.7)	(126.4)	(67.6)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	9.2	(34.9)	31.2	(83.0)
Net impairment losses on available-for-sale securities			(95.2)	(150.6)
Net realized capital gains (losses)	87.7	(30.7)	81.2	(51.0)
Total revenues	2,704.7	2,093.6	6,919.2	6,611.9
Expenses
Benefits, claims and settlement expenses	1,647.0	1,114.9	3,969.5	3,497.7
Dividends to policyholders	49.7	52.2	149.5	158.7
Operating expenses	826.6	775.4	2,106.7	2,232.7
Total expenses	2,523.3	1,942.5	6,225.7	5,889.1
Income (loss) before income taxes	181.4	151.1	693.5	722.8
Income taxes (benefits)	(9.9)	76.6	99.2	190.3
Net income (loss)	191.3	74.5	594.3	532.5
Net income (loss) attributable to noncontrolling interest	3.4	(5.6)	15.3	36.6
Net income (loss) attributable to Principal Financial Group, Inc.	187.9	80.1	579.0	495.9
Preferred stock dividends	8.2	8.2	24.7	24.7
Net income (loss) available to common stockholders	179.7	71.9	554.3	471.2
Net income (loss)	191.3	74.5	594.3	532.5
Other comprehensive income (loss)	331.1	(279.5)	623.8	155.1
Comprehensive income (loss)	522.4	(205.0)	1,218.1	687.6
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues			0.3	0.1
Net investment income (loss)			2.7	1.5
Total revenues			3.0	1.6
Expenses
Operating expenses			90.8	86.4
Total expenses			90.8	86.4
Income (loss) before income taxes			(87.8)	(84.8)
Income taxes (benefits)			(34.4)	(32.4)
Equity in the net income (loss) of subsidiaries			632.4	548.3
Net income (loss)			579.0	495.9
Net income (loss) attributable to Principal Financial Group, Inc.			579.0	495.9
Preferred stock dividends			24.7	24.7
Net income (loss) available to common stockholders			554.3	471.2
Net income (loss)			579.0	495.9
Other comprehensive income (loss)			570.3	175.8
Comprehensive income (loss)			1,149.3	671.7
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			2,265.7	1,993.2
Fees and other revenues			1,115.0	1,190.4
Net investment income (loss)			1,869.8	1,961.0
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(296.9)	482.0
Total other-than-temporary impairment losses on available-for-sale securities			(111.5)	(51.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			27.1	(90.0)
Net impairment losses on available-for-sale securities			(84.4)	(141.8)
Net realized capital gains (losses)			(381.3)	340.2
Total revenues			4,869.2	5,484.8
Expenses
Benefits, claims and settlement expenses			3,542.3	3,065.3
Dividends to policyholders			149.5	158.7
Operating expenses			1,286.3	1,511.1
Total expenses			4,978.1	4,735.1
Income (loss) before income taxes			(108.9)	749.7
Income taxes (benefits)			(126.4)	263.1
Equity in the net income (loss) of subsidiaries			438.6	(63.0)
Net income (loss)			456.1	423.6
Net income (loss) attributable to Principal Financial Group, Inc.			456.1	423.6
Net income (loss) available to common stockholders			456.1	423.6
Net income (loss)			456.1	423.6
Other comprehensive income (loss)			546.2	239.7
Comprehensive income (loss)			1,002.3	663.3
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			253.6	228.5
Fees and other revenues			1,018.9	928.8
Net investment income (loss)			521.9	562.4
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			496.8	(386.2)
Total other-than-temporary impairment losses on available-for-sale securities			(14.8)	(15.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			4.1	7.0
Net impairment losses on available-for-sale securities			(10.7)	(8.8)
Net realized capital gains (losses)			486.1	(395.0)
Total revenues			2,280.5	1,324.7
Expenses
Benefits, claims and settlement expenses			436.7	442.4
Operating expenses			925.8	827.2
Total expenses			1,362.5	1,269.6
Income (loss) before income taxes			918.0	55.1
Income taxes (benefits)			260.5	(39.2)
Equity in the net income (loss) of subsidiaries			(9.7)	490.7
Net income (loss)			647.8	585.0
Net income (loss) attributable to noncontrolling interest			15.4	36.7
Net income (loss) attributable to Principal Financial Group, Inc.			632.4	548.3
Net income (loss) available to common stockholders			632.4	548.3
Net income (loss)			647.8	585.0
Other comprehensive income (loss)			110.4	(89.9)
Comprehensive income (loss)			758.2	495.1
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(225.1)	(226.7)
Net investment income (loss)			15.2	23.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(23.5)	3.8
Total other-than-temporary impairment losses on available-for-sale securities			(0.1)
Net impairment losses on available-for-sale securities			(0.1)
Net realized capital gains (losses)			(23.6)	3.8
Total revenues			(233.5)	(199.2)
Expenses
Benefits, claims and settlement expenses			(9.5)	(10.0)
Operating expenses			(196.2)	(192.0)
Total expenses			(205.7)	(202.0)
Income (loss) before income taxes			(27.8)	2.8
Income taxes (benefits)			(0.5)	(1.2)
Equity in the net income (loss) of subsidiaries			(1,061.3)	(976.0)
Net income (loss)			(1,088.6)	(972.0)
Net income (loss) attributable to noncontrolling interest			(0.1)	(0.1)
Net income (loss) attributable to Principal Financial Group, Inc.			(1,088.5)	(971.9)
Net income (loss) available to common stockholders			(1,088.5)	(971.9)
Net income (loss)			(1,088.6)	(972.0)
Other comprehensive income (loss)			(603.1)	(170.5)
Comprehensive income (loss)			$ (1,691.7)	$ (1,142.5)