Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Assets
Fixed maturities, available-for-sale	$ 51,533.9	$ 49,006.7
Fixed maturities, trading	808.0	971.7
Equity securities, available-for-sale	143.6	77.1
Equity securities, trading	237.6	404.8
Mortgage loans	11,297.9	10,727.2
Real estate	1,208.6	1,092.9
Policy loans	866.6	885.1
Investment in unconsolidated entities	837.7	827.3
Other investments	2,334.4	2,158.5
Cash and cash equivalents	2,279.0	2,833.9	1,434.2	1,877.4
Accrued investment income	614.4	615.2
Premiums due and other receivables	1,192.2	1,196.5
Deferred policy acquisition costs	2,558.5	2,428.0
Property and equipment	468.4	457.2
Goodwill	548.9	482.3
Other intangibles	927.4	890.6
Separate account assets	80,160.5	71,364.4
Other assets	1,175.7	942.3
Total assets	159,193.3	147,361.7
Liabilities
Contractholder funds	37,312.2	37,676.4
Future policy benefits and claims	21,952.0	20,210.4
Other policyholder funds	720.8	548.6
Short-term debt	28.5	105.2
Long-term debt	2,180.0	1,564.8
Income taxes currently payable	6.6	3.1
Deferred income taxes	951.5	208.7
Separate account liabilities	80,160.5	71,364.4
Other liabilities	5,974.3	6,286.2
Total liabilities	149,286.4	137,967.8
Redeemable noncontrolling interest	61.0	22.2
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,712.2	9,634.7
Retained earnings (accumulated deficit)	4,784.3	4,402.3
Accumulated other comprehensive income (loss)	880.8	258.0
Treasury stock, at cost (159.7 million and 149.2 million shares in 2012 and 2011)	(5,554.4)	(5,281.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,827.5	9,017.9
Noncontrolling interest	18.4	353.8
Total stockholders' equity	9,845.9	9,371.7	9,682.6	9,306.4
Total liabilities and stockholders' equity	159,193.3	147,361.7
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading	173.7	268.7
Investment in unconsolidated entities	10,588.7	9,828.0
Other investments	6.0	7.0
Cash and cash equivalents	975.2	226.7	369.9	370.9
Accrued investment income	0.2	1.8
Premiums due and other receivables	30.1
Other assets	56.5	14.8
Total assets	11,830.4	10,347.0
Liabilities
Long-term debt	1,950.1	1,351.7
Income taxes currently payable		(18.6)
Deferred income taxes		(22.5)
Other liabilities	52.8	18.5
Total liabilities	2,002.9	1,329.1
Stockholders' equity
Common stock	4.5	4.5
Additional paid-in capital	9,712.2	9,634.7
Retained earnings (accumulated deficit)	4,784.3	4,402.3
Accumulated other comprehensive income (loss)	880.8	258.0
Treasury stock, at cost (159.7 million and 149.2 million shares in 2012 and 2011)	(5,554.4)	(5,281.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,827.5	9,017.9
Total stockholders' equity	9,827.5	9,017.9
Total liabilities and stockholders' equity	11,830.4	10,347.0
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	10,488.8	9,762.9
Other investments	29.0	3.0
Cash and cash equivalents	459.5	702.4	548.0	519.7
Other assets	49.2	10.4
Total assets	11,026.5	10,478.7
Liabilities
Short-term debt		50.0
Income taxes currently payable	2.1	(0.9)
Deferred income taxes		(22.9)
Other liabilities	435.7	624.5
Total liabilities	437.8	650.7
Stockholders' equity
Additional paid-in capital	7,906.0	7,870.2
Retained earnings (accumulated deficit)	1,765.2	1,660.3
Accumulated other comprehensive income (loss)	917.5	297.5
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,588.7	9,828.0
Total stockholders' equity	10,588.7	9,828.0
Total liabilities and stockholders' equity	11,026.5	10,478.7
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	51,533.9	49,006.7
Fixed maturities, trading	634.3	703.0
Equity securities, available-for-sale	143.6	77.1
Equity securities, trading	237.6	404.8
Mortgage loans	11,297.9	10,727.2
Real estate	1,208.6	1,092.9
Policy loans	866.6	885.1
Investment in unconsolidated entities	837.7	827.2
Other investments	2,299.4	2,148.5
Cash and cash equivalents	1,558.9	2,787.9	1,545.3	1,821.7
Accrued investment income	614.2	613.4
Premiums due and other receivables	1,161.8	1,195.2
Deferred policy acquisition costs	2,558.5	2,428.0
Property and equipment	468.4	457.2
Goodwill	548.9	482.3
Other intangibles	927.4	890.6
Separate account assets	80,160.5	71,364.4
Other assets	1,207.0	926.1
Total assets	158,265.2	147,017.6
Liabilities
Contractholder funds	37,312.2	37,676.4
Future policy benefits and claims	21,952.0	20,210.4
Other policyholder funds	720.8	548.6
Short-term debt	309.6	318.9
Long-term debt	229.9	213.1
Income taxes currently payable	42.5	12.0
Deferred income taxes	1,035.1	270.8
Separate account liabilities	80,160.5	71,364.4
Other liabilities	5,934.4	6,264.1
Total liabilities	147,697.0	136,878.7
Redeemable noncontrolling interest	61.0	22.2
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	7,901.5	7,543.4
Retained earnings (accumulated deficit)	1,692.3	1,907.5
Accumulated other comprehensive income (loss)	879.2	296.2
Treasury stock, at cost (159.7 million and 149.2 million shares in 2012 and 2011)	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,488.8	9,762.9
Noncontrolling interest	18.4	353.8
Total stockholders' equity	10,507.2	10,116.7
Total liabilities and stockholders' equity	158,265.2	147,017.6
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(21,077.5)	(19,590.8)
Cash and cash equivalents	(714.6)	(883.1)	(1,029.0)	(834.9)
Premiums due and other receivables	0.3	1.3
Other assets	(137.0)	(9.0)
Total assets	(21,928.8)	(20,481.6)
Liabilities
Short-term debt	(281.1)	(263.7)
Income taxes currently payable	(38.0)	10.6
Deferred income taxes	(83.6)	(16.7)
Other liabilities	(448.6)	(620.9)
Total liabilities	(851.3)	(890.7)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(15,807.5)	(15,413.6)
Retained earnings (accumulated deficit)	(3,457.5)	(3,567.8)
Accumulated other comprehensive income (loss)	(1,796.7)	(593.7)
Treasury stock, at cost (159.7 million and 149.2 million shares in 2012 and 2011)	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(21,077.5)	(19,590.9)
Total stockholders' equity	(21,077.5)	(19,590.9)
Total liabilities and stockholders' equity	(21,928.8)	(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