Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues
Premiums and other considerations	$ 737.2	$ 681.3	$ 1,431.9	$ 1,361.1
Fees and other revenues	803.8	636.1	1,537.4	1,234.1
Net investment income (loss)	749.7	801.0	1,539.0	1,625.8
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities	(53.4)	32.2	(79.8)	54.3
Total other-than-temporary impairment losses on available-for-sale securities	(24.6)	(49.1)	(69.3)	(82.8)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(2.1)	17.1	18.1	22.0
Net impairment losses on available-for-sale securities			(51.2)	(60.8)
Net realized capital gains (losses)	(80.1)	0.2	(131.0)	(6.5)
Total revenues	2,210.6	2,118.6	4,377.3	4,214.5
Expenses
Benefits, claims and settlement expenses	1,095.7	1,110.0	2,190.2	2,322.5
Dividends to policyholders	47.5	49.5	95.8	99.8
Operating expenses	801.8	729.6	1,597.5	1,284.7
Total expenses	1,945.0	1,889.1	3,883.5	3,707.0
Income (loss) before income taxes	265.6	229.5	493.8	507.5
Income taxes (benefits)	29.0	50.9	67.2	107.6
Net income (loss)	236.6	178.6	426.6	399.9
Net income (loss) attributable to noncontrolling interest	6.0	2.7	9.5	11.9
Net income (loss) attributable to Principal Financial Group, Inc.	230.6	175.9	417.1	388.0
Preferred stock dividends	8.3	8.3	16.5	16.5
Net income (loss) available to common stockholders	222.3	167.6	400.6	371.5
Net income (loss)	236.6	178.6	426.6	399.9
Other comprehensive income (loss)	(629.9)	65.0	(650.3)	290.2
Comprehensive income (loss)	(393.3)	243.6	(223.7)	690.1
Principal Financial Group, Inc. Parent Only
Revenues
Fees and other revenues				0.2
Net investment income (loss)			0.1	1.2
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			6.3
Net realized capital gains (losses)			6.3
Total revenues			6.4	1.4
Expenses
Operating expenses			70.2	60.0
Total expenses			70.2	60.0
Income (loss) before income taxes			(63.8)	(58.6)
Income taxes (benefits)			(25.6)	(22.9)
Equity in the net income (loss) of subsidiaries			455.3	423.7
Net income (loss)			417.1	388.0
Net income (loss) attributable to Principal Financial Group, Inc.			417.1	388.0
Preferred stock dividends			16.5	16.5
Net income (loss) available to common stockholders			400.6	371.5
Net income (loss)			417.1	388.0
Other comprehensive income (loss)			(700.5)	247.0
Comprehensive income (loss)			(283.4)	635.0
Principal Life Insurance Company Only
Revenues
Premiums and other considerations			1,243.9	1,185.9
Fees and other revenues			837.6	718.7
Net investment income (loss)			1,187.1	1,257.6
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			(287.9)	18.3
Total other-than-temporary impairment losses on available-for-sale securities			(63.6)	(72.0)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			19.2	16.2
Net impairment losses on available-for-sale securities			(44.4)	(55.8)
Net realized capital gains (losses)			(332.3)	(37.5)
Total revenues			2,936.3	3,124.7
Expenses
Benefits, claims and settlement expenses			1,910.7	2,013.8
Dividends to policyholders			95.8	99.8
Operating expenses			930.5	749.0
Total expenses			2,937.0	2,862.6
Income (loss) before income taxes			(0.7)	262.1
Income taxes (benefits)			(55.2)	60.5
Equity in the net income (loss) of subsidiaries			275.4	119.5
Net income (loss)			329.9	321.1
Net income (loss) attributable to Principal Financial Group, Inc.			329.9	321.1
Net income (loss) available to common stockholders			329.9	321.1
Net income (loss)			329.9	321.1
Other comprehensive income (loss)			(464.3)	275.0
Comprehensive income (loss)			(134.4)	596.1
Principal Financial Services, Inc. and Other Subsidiaries Combined
Revenues
Premiums and other considerations			188.0	175.2
Fees and other revenues			870.6	665.0
Net investment income (loss)			337.8	361.7
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			201.7	52.9
Total other-than-temporary impairment losses on available-for-sale securities			(5.7)	(10.7)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income			(1.1)	5.8
Net impairment losses on available-for-sale securities			(6.8)	(4.9)
Net realized capital gains (losses)			194.9	48.0
Total revenues			1,591.3	1,249.9
Expenses
Benefits, claims and settlement expenses			285.7	315.0
Operating expenses			745.5	606.3
Total expenses			1,031.2	921.3
Income (loss) before income taxes			560.1	328.6
Income taxes (benefits)			148.2	70.1
Equity in the net income (loss) of subsidiaries			53.0	177.2
Net income (loss)			464.9	435.7
Net income (loss) attributable to noncontrolling interest			9.6	12.0
Net income (loss) attributable to Principal Financial Group, Inc.			455.3	423.7
Net income (loss) available to common stockholders			455.3	423.7
Net income (loss)			464.9	435.7
Other comprehensive income (loss)			(198.7)	23.2
Comprehensive income (loss)			266.2	458.9
Eliminations, Notes Guarantor
Revenues
Fees and other revenues			(170.8)	(149.8)
Net investment income (loss)			14.0	5.3
Net realized capital gains (losses), excluding impairment losses on available-for-sale securities			0.1	(16.9)
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)			0.1	(17.0)
Total revenues			(156.7)	(161.5)
Expenses
Benefits, claims and settlement expenses			(6.2)	(6.3)
Operating expenses			(148.7)	(130.6)
Total expenses			(154.9)	(136.9)
Income (loss) before income taxes			(1.8)	(24.6)
Income taxes (benefits)			(0.2)	(0.1)
Equity in the net income (loss) of subsidiaries			(783.7)	(720.4)
Net income (loss)			(785.3)	(744.9)
Net income (loss) attributable to noncontrolling interest			(0.1)	(0.1)
Net income (loss) attributable to Principal Financial Group, Inc.			(785.2)	(744.8)
Net income (loss) available to common stockholders			(785.2)	(744.8)
Net income (loss)			(785.3)	(744.9)
Other comprehensive income (loss)			713.2	(255.0)
Comprehensive income (loss)			$ (72.1)	$ (999.9)