Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets
Fixed maturities, available-for-sale	$ 51,084.1	$ 50,939.3
Fixed maturities, trading	628.9	626.7
Equity securities, available-for-sale	147.0	136.5
Equity securities, trading	732.2	252.8
Mortgage loans	11,577.9	11,519.7
Real estate	1,202.0	1,180.3
Policy loans	866.5	864.9
Investment in unconsolidated entities	881.4	869.0
Other investments	2,305.8	2,422.1
Cash and cash equivalents	1,661.2	4,177.2	1,651.9	2,833.9
Accrued investment income	584.5	584.4
Premiums due and other receivables	1,175.2	1,084.4
Deferred acquisition costs	2,715.5	2,590.0
Property and equipment	472.6	464.2
Goodwill	1,197.4	543.4		482.3
Other intangibles	1,590.3	914.7
Separate account assets	120,906.1	81,653.8
Other assets	1,034.3	1,006.8
Total assets	200,762.9	161,830.2
Liabilities
Contractholder funds	36,701.6	37,786.5
Future policy benefits and claims	22,689.5	22,436.2
Other policyholder funds	811.2	716.4
Short-term debt	46.5	40.8
Long-term debt	2,790.5	2,671.3
Income taxes currently payable	9.8	15.3
Deferred income taxes	791.4	600.0
Separate account liabilities	120,906.1	81,653.8
Other liabilities	6,130.8	6,146.1
Total liabilities	190,877.4	152,066.4
Redeemable noncontrolling interest	58.9	60.4	23.1	22.2
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,771.5	9,730.9
Retained earnings (accumulated deficit)	4,971.7	4,862.0
Accumulated other comprehensive income (loss)	621.0	640.3
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	(5,645.3)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,723.6	9,683.4
Noncontrolling interest	103.0	20.0
Total stockholders' equity	9,826.6	9,703.4	9,660.0	9,306.2
Total liabilities and stockholders' equity	200,762.9	161,830.2
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Investment in unconsolidated entities	12,036.1	11,853.3
Other investments	9.0	11.1
Cash and cash equivalents	112.7	207.1	378.3	226.7
Premiums due and other receivables		0.1
Other assets	66.2	78.0
Total assets	12,224.0	12,160.1
Liabilities
Long-term debt	2,448.6	2,448.6
Other liabilities	51.8	28.1
Total liabilities	2,500.4	2,476.7
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,771.5	9,730.9
Retained earnings (accumulated deficit)	4,971.7	4,862.0
Accumulated other comprehensive income (loss)	621.0	640.3
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	(5,645.3)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,723.6	9,683.4
Total stockholders' equity	9,723.6	9,683.4
Total liabilities and stockholders' equity	12,224.0	12,160.1
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	10,819.4	10,632.1
Other investments	52.1	39.6
Cash and cash equivalents	584.8	612.5	621.9	702.4
Premiums due and other receivables	990.8	1,122.1
Other assets	82.8	51.0
Total assets	12,529.9	12,457.3
Liabilities
Income taxes currently payable	18.3	0.1
Other liabilities	475.5	603.9
Total liabilities	493.8	604.0
Stockholders' equity
Additional paid-in capital	9,394.8	9,393.8
Retained earnings (accumulated deficit)	1,986.1	1,783.4
Accumulated other comprehensive income (loss)	655.2	676.1
Total stockholders' equity attributable to Principal Financial Group, Inc.	12,036.1	11,853.3
Total stockholders' equity	12,036.1	11,853.3
Total liabilities and stockholders' equity	12,529.9	12,457.3
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	51,084.1	50,939.3
Fixed maturities, trading	628.9	616.2
Equity securities, available-for-sale	147.0	136.5
Equity securities, trading	732.2	252.8
Mortgage loans	11,577.9	11,519.7
Real estate	1,202.0	1,180.3
Policy loans	866.5	864.9
Investment in unconsolidated entities	872.7	860.2
Other investments	2,244.7	2,371.4
Cash and cash equivalents	1,755.9	4,241.3	1,587.0	2,787.9
Accrued investment income	584.5	584.4
Premiums due and other receivables	2,176.4	2,206.7
Deferred acquisition costs	2,715.5	2,590.0
Property and equipment	472.6	464.2
Goodwill	1,197.4	543.4
Other intangibles	1,590.3	914.7
Separate account assets	120,906.1	81,653.8
Other assets	1,071.0	1,003.5
Total assets	201,825.7	162,943.3
Liabilities
Contractholder funds	36,701.6	37,786.5
Future policy benefits and claims	22,689.5	22,436.2
Other policyholder funds	811.2	716.4
Short-term debt	2,353.4	2,564.1
Long-term debt	341.9	222.7
Income taxes currently payable	49.1	47.2
Deferred income taxes	899.8	686.1
Separate account liabilities	120,906.1	81,653.8
Other liabilities	6,091.8	6,117.8
Total liabilities	190,844.4	152,230.8
Redeemable noncontrolling interest	58.9	60.4
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	8,306.5	8,287.7
Retained earnings (accumulated deficit)	1,854.8	1,666.7
Accumulated other comprehensive income (loss)	642.3	661.9
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,819.4	10,632.1
Noncontrolling interest	103.0	20.0
Total stockholders' equity	10,922.4	10,652.1
Total liabilities and stockholders' equity	201,825.7	162,943.3
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(22,846.8)	(22,476.6)
Cash and cash equivalents	(792.2)	(883.7)	(935.3)	(883.1)
Premiums due and other receivables	(1,992.0)	(2,244.5)
Other assets	(185.7)	(125.7)
Total assets	(25,816.7)	(25,730.5)
Liabilities
Short-term debt	(2,306.9)	(2,523.3)
Income taxes currently payable	(57.6)	(32.0)
Deferred income taxes	(108.4)	(86.1)
Other liabilities	(488.3)	(603.7)
Total liabilities	(2,961.2)	(3,245.1)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(17,701.3)	(17,681.5)
Retained earnings (accumulated deficit)	(3,840.9)	(3,450.1)
Accumulated other comprehensive income (loss)	(1,297.5)	(1,338.0)
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(22,855.5)	(22,485.4)
Total stockholders' equity	(22,855.5)	(22,485.4)
Total liabilities and stockholders' equity	(25,816.7)	(25,730.5)
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