Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets
Fixed maturities, available-for-sale	$ 49,006.7	$ 48,636.3
Fixed maturities, trading	971.7	1,120.3
Equity securities, available-for-sale	77.1	169.9
Equity securities, trading	404.8	316.9
Mortgage loans	10,727.2	11,125.1
Real estate	1,092.9	1,063.5
Policy loans	885.1	903.9
Investment in unconsolidated entities	829.5	736.0
Other investments	2,158.5	1,905.6
Cash and cash equivalents	2,833.9	1,877.4	2,240.4	2,608.0
Accrued investment income	615.2	666.1
Premiums due and other receivables	1,245.2	1,063.0
Deferred policy acquisition costs	3,313.5	3,529.8	3,681.4	4,153.0
Property and equipment	457.2	458.7
Goodwill	482.3	345.4	386.4
Other intangibles	890.6	834.6
Separate account assets	71,364.4	69,555.3
Other assets	942.2	1,323.3
Total assets	148,298.0	145,631.1
Liabilities
Contractholder funds	37,676.4	37,301.1
Future policy benefits and claims	20,207.9	20,046.3
Other policyholder funds	543.7	592.2
Short-term debt	105.2	107.9
Long-term debt	1,564.8	1,583.7
Income taxes currently payable	3.1	6.2
Deferred income taxes	533.4	409.9
Separate account liabilities	71,364.4	69,555.3
Other liabilities	6,286.1	6,143.5
Total liabilities	138,285.0	135,746.1
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,634.7	9,563.8
Retained earnings (deficit)	5,077.5	4,612.3
Accumulated other comprehensive income (loss)	201.9	272.4
Treasury stock, at cost (149.2 million and 128.1 million shares in 2011 and 2010)	(5,281.7)	(4,725.3)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,637.0	9,727.8
Noncontrolling interest	376.0	157.2
Total stockholders' equity	10,013.0	9,885.0	8,016.4	2,569.3
Total liabilities and stockholders' equity	148,298.0	145,631.1
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, available-for-sale		199.9
Fixed maturities, trading	268.7	274.9
Investment in unconsolidated entities	10,447.1	10,195.1
Other investments	7.0	5.6
Cash and cash equivalents	226.7	370.9	304.6	(2.0)
Accrued investment income	1.8	0.8
Other assets	14.8	13.6
Total assets	10,966.1	11,060.8
Liabilities
Long-term debt	1,351.7	1,351.7
Income taxes currently payable	(18.6)	(18.8)
Deferred income taxes	(22.5)	(21.6)
Other liabilities	18.5	21.7
Total liabilities	1,329.1	1,333.0
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,634.7	9,563.8
Retained earnings (deficit)	5,077.5	4,612.3
Accumulated other comprehensive income (loss)	201.9	272.4
Treasury stock, at cost (149.2 million and 128.1 million shares in 2011 and 2010)	(5,281.7)	(4,725.3)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,637.0	9,727.8
Total stockholders' equity	9,637.0	9,727.8
Total liabilities and stockholders' equity	10,966.1	11,060.8
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	10,382.0	10,209.0
Other investments	3.0	45.5
Cash and cash equivalents	702.4	519.7	534.4	546.0
Other assets	10.4	9.8
Total assets	11,097.8	10,784.0
Liabilities
Short-term debt	50.0	50.0
Income taxes currently payable	(0.9)	(2.3)
Deferred income taxes	(22.8)	(8.7)
Other liabilities	624.4	549.9
Total liabilities	650.7	588.9
Stockholders' equity
Additional paid-in capital	7,870.2	8,334.0
Retained earnings (deficit)	2,335.6	1,546.3
Accumulated other comprehensive income (loss)	241.3	314.8
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,447.1	10,195.1
Total stockholders' equity	10,447.1	10,195.1
Total liabilities and stockholders' equity	11,097.8	10,784.0
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	49,006.7	48,436.4
Fixed maturities, trading	703.0	845.4
Equity securities, available-for-sale	77.1	169.9
Equity securities, trading	404.8	316.9
Mortgage loans	10,727.2	11,125.1
Real estate	1,092.9	1,063.5
Policy loans	885.1	903.9
Investment in unconsolidated entities	829.5	735.8
Other investments	2,148.5	1,854.5
Cash and cash equivalents	2,787.9	1,821.7	2,256.8	2,728.5
Accrued investment income	613.4	665.3
Premiums due and other receivables	1,243.9	1,066.1
Deferred policy acquisition costs	3,313.5	3,529.8
Property and equipment	457.2	458.7
Goodwill	482.3	345.4
Other intangibles	890.6	834.6
Separate account assets	71,364.4	69,555.3
Other assets	926.0	1,302.4
Total assets	147,954.0	145,030.7
Liabilities
Contractholder funds	37,676.4	37,301.1
Future policy benefits and claims	20,207.9	20,046.3
Other policyholder funds	543.7	592.2
Short-term debt	318.9	352.3
Long-term debt	213.1	232.0
Income taxes currently payable	12.0	11.6
Deferred income taxes	595.4	455.7
Separate account liabilities	71,364.4	69,555.3
Other liabilities	6,264.2	6,118.0
Total liabilities	137,196.0	134,664.5
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	7,543.4	7,730.0
Retained earnings (deficit)	2,582.7	2,142.4
Accumulated other comprehensive income (loss)	240.1	320.8
Treasury stock, at cost (149.2 million and 128.1 million shares in 2011 and 2010)	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,382.0	10,209.0
Noncontrolling interest	376.0	157.2
Total stockholders' equity	10,758.0	10,366.2
Total liabilities and stockholders' equity	147,954.0	145,030.7
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(20,829.1)	(20,403.9)
Cash and cash equivalents	(883.1)	(834.9)	(855.4)	(664.5)
Premiums due and other receivables	1.3	(3.1)
Other assets	(9.0)	(2.5)
Total assets	(21,719.9)	(21,244.4)
Liabilities
Short-term debt	(263.7)	(294.4)
Income taxes currently payable	10.6	15.7
Deferred income taxes	(16.7)	(15.5)
Other liabilities	(621.0)	(546.1)
Total liabilities	(890.8)	(840.3)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(15,413.6)	(16,064.0)
Retained earnings (deficit)	(4,918.3)	(3,688.7)
Accumulated other comprehensive income (loss)	(481.4)	(635.6)
Treasury stock, at cost (149.2 million and 128.1 million shares in 2011 and 2010)	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(20,829.1)	(20,404.1)
Total stockholders' equity	(20,829.1)	(20,404.1)
Total liabilities and stockholders' equity	(21,719.9)	(21,244.4)
Series A
Stockholders' equity
Preferred stock, value
Series B
Stockholders' equity
Preferred stock, value	0.1	0.1
Series B | Principal Financial Group, Inc. Parent Only
Stockholders' equity
Preferred stock, value	$ 0.1	$ 0.1