Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Assets
Fixed maturities, available-for-sale	$ 49,793.6	$ 49,006.7
Fixed maturities, trading	776.5	971.7
Equity securities, available-for-sale	139.0	77.1
Equity securities, trading	224.3	404.8
Mortgage loans	11,158.6	10,727.2
Real estate	1,174.1	1,092.9
Policy loans	867.8	885.1
Investment in unconsolidated entities	821.9	827.3
Other investments	2,274.9	2,158.5
Cash and cash equivalents	1,646.6	2,833.9	2,169.6	1,877.4
Accrued investment income	589.5	615.2
Premiums due and other receivables	1,097.0	1,196.5
Deferred policy acquisition costs	2,663.8	2,428.0
Property and equipment	469.7	457.2
Goodwill	542.0	482.3
Other intangibles	934.9	890.6
Separate account assets	75,950.5	71,364.4
Other assets	926.0	942.3
Total assets	152,050.7	147,361.7
Liabilities
Contractholder funds	36,727.5	37,676.4
Future policy benefits and claims	20,791.4	20,210.4
Other policyholder funds	663.4	548.6
Short-term debt	262.9	105.2
Long-term debt	1,576.9	1,564.8
Income taxes currently payable	2.4	3.1
Deferred income taxes	568.7	208.7
Separate account liabilities	75,950.5	71,364.4
Other liabilities	6,011.6	6,286.2
Total liabilities	142,555.3	137,967.8
Redeemable noncontrolling interest	60.5	22.2
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,685.4	9,634.7
Retained earnings (accumulated deficit)	4,667.1	4,402.3
Accumulated other comprehensive income (loss)	550.5	258.0
Treasury stock, at cost (157.0 million and 149.2 million shares in 2012 and 2011)	(5,484.9)	(5,281.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,422.7	9,017.9
Noncontrolling interest	12.2	353.8
Total stockholders' equity	9,434.9	9,371.7	10,042.2	9,306.4
Total liabilities and stockholders' equity	152,050.7	147,361.7
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading	152.2	268.7
Investment in unconsolidated entities	10,216.3	9,828.0
Other investments	5.8	7.0
Cash and cash equivalents	374.4	226.7	786.5	370.9
Accrued investment income	0.2	1.8
Other assets	13.7	14.8
Total assets	10,762.6	10,347.0
Liabilities
Long-term debt	1,351.7	1,351.7
Income taxes currently payable	(20.3)	(18.6)
Deferred income taxes	(16.8)	(22.5)
Other liabilities	25.3	18.5
Total liabilities	1,339.9	1,329.1
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,685.4	9,634.7
Retained earnings (accumulated deficit)	4,667.1	4,402.3
Accumulated other comprehensive income (loss)	550.5	258.0
Treasury stock, at cost (157.0 million and 149.2 million shares in 2012 and 2011)	(5,484.9)	(5,281.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,422.7	9,017.9
Total stockholders' equity	9,422.7	9,017.9
Total liabilities and stockholders' equity	10,762.6	10,347.0
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	10,164.8	9,762.9
Other investments	23.2	3.0
Cash and cash equivalents	618.4	702.4	746.8	519.7
Other assets	11.5	10.4
Total assets	10,817.9	10,478.7
Liabilities
Short-term debt		50.0
Income taxes currently payable	0.3	(0.9)
Deferred income taxes	(35.1)	(22.9)
Other liabilities	636.4	624.5
Total liabilities	601.6	650.7
Stockholders' equity
Additional paid-in capital	7,892.8	7,870.2
Retained earnings (accumulated deficit)	1,735.5	1,660.3
Accumulated other comprehensive income (loss)	588.0	297.5
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,216.3	9,828.0
Total stockholders' equity	10,216.3	9,828.0
Total liabilities and stockholders' equity	10,817.9	10,478.7
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	49,793.6	49,006.7
Fixed maturities, trading	624.3	703.0
Equity securities, available-for-sale	139.0	77.1
Equity securities, trading	224.3	404.8
Mortgage loans	11,158.6	10,727.2
Real estate	1,174.1	1,092.9
Policy loans	867.8	885.1
Investment in unconsolidated entities	821.9	827.2
Other investments	2,245.9	2,148.5
Cash and cash equivalents	1,599.2	2,787.9	1,686.7	1,821.7
Accrued investment income	589.3	613.4
Premiums due and other receivables	1,095.7	1,195.2
Deferred policy acquisition costs	2,663.8	2,428.0
Property and equipment	469.7	457.2
Goodwill	542.0	482.3
Other intangibles	934.9	890.6
Separate account assets	75,950.5	71,364.4
Other assets	912.2	926.1
Total assets	151,806.8	147,017.6
Liabilities
Contractholder funds	36,727.5	37,676.4
Future policy benefits and claims	20,791.4	20,210.4
Other policyholder funds	663.4	548.6
Short-term debt	574.3	318.9
Long-term debt	225.2	213.1
Income taxes currently payable	11.9	12.0
Deferred income taxes	640.2	270.8
Separate account liabilities	75,950.5	71,364.4
Other liabilities	5,984.9	6,264.1
Total liabilities	141,569.3	136,878.7
Redeemable noncontrolling interest	60.5	22.2
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	7,621.0	7,543.4
Retained earnings (accumulated deficit)	1,952.0	1,907.5
Accumulated other comprehensive income (loss)	576.0	296.2
Treasury stock, at cost (157.0 million and 149.2 million shares in 2012 and 2011)	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,164.8	9,762.9
Noncontrolling interest	12.2	353.8
Total stockholders' equity	10,177.0	10,116.7
Total liabilities and stockholders' equity	151,806.8	147,017.6
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(20,381.1)	(19,590.8)
Cash and cash equivalents	(945.4)	(883.1)	(1,050.4)	(834.9)
Premiums due and other receivables	1.3	1.3
Other assets	(11.4)	(9.0)
Total assets	(21,336.6)	(20,481.6)
Liabilities
Short-term debt	(311.4)	(263.7)
Income taxes currently payable	10.5	10.6
Deferred income taxes	(19.6)	(16.7)
Other liabilities	(635.0)	(620.9)
Total liabilities	(955.5)	(890.7)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(15,513.8)	(15,413.6)
Retained earnings (accumulated deficit)	(3,687.5)	(3,567.8)
Accumulated other comprehensive income (loss)	(1,164.0)	(593.7)
Treasury stock, at cost (157.0 million and 149.2 million shares in 2012 and 2011)	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(20,381.1)	(19,590.9)
Total stockholders' equity	(20,381.1)	(19,590.9)
Total liabilities and stockholders' equity	(21,336.6)	(20,481.6)
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