Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Assets
Fixed maturities, available-for-sale	$ 49,191.6	$ 50,939.3
Fixed maturities, trading	589.8	626.7
Equity securities, available-for-sale	135.3	136.5
Equity securities, trading	636.7	252.8
Mortgage loans	12,121.7	11,519.7
Real estate	1,264.8	1,180.3
Policy loans	865.3	864.9
Investment in unconsolidated entities	879.3	869.0
Other investments	2,097.0	2,422.1
Cash and cash equivalents	1,110.5	4,177.2	1,646.6	2,833.9
Accrued investment income	565.4	584.4
Premiums due and other receivables	1,219.0	1,084.4
Deferred acquisition costs	2,925.4	2,590.0
Property and equipment	476.4	464.2
Goodwill	1,138.5	543.4
Other intangibles	1,517.3	914.7
Separate account assets	118,740.2	81,653.8
Other assets	1,038.5	1,006.8
Total assets	196,512.7	161,830.2
Liabilities
Contractholder funds	36,269.7	37,786.5
Future policy benefits and claims	22,129.5	22,436.2
Other policyholder funds	739.5	716.4
Short-term debt	175.3	40.8
Long-term debt	2,578.6	2,671.3
Income taxes currently payable	7.2	15.3
Deferred income taxes	578.7	600.0
Separate account liabilities	118,740.2	81,653.8
Other liabilities	5,831.5	6,146.1
Total liabilities	187,050.2	152,066.4
Redeemable noncontrolling interest	53.6	60.4	60.5	22.2
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,819.8	9,730.9
Retained earnings (accumulated deficit)	5,125.2	4,862.0
Accumulated other comprehensive income (loss)	(0.5)	640.3
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	(5,645.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,303.4	9,683.4
Noncontrolling interest	105.5	20.0
Total stockholders' equity	9,408.9	9,703.4	9,363.8	9,306.2
Total liabilities and stockholders' equity	196,512.7	161,830.2
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Investment in unconsolidated entities	11,693.7	11,853.3
Other investments	9.0	11.1
Cash and cash equivalents	18.5	207.1	374.4	226.7
Premiums due and other receivables		0.1
Other assets	64.1	78.0
Total assets	11,785.3	12,160.1
Liabilities
Long-term debt	2,448.7	2,448.6
Other liabilities	33.2	28.1
Total liabilities	2,481.9	2,476.7
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,819.8	9,730.9
Retained earnings (accumulated deficit)	5,125.2	4,862.0
Accumulated other comprehensive income (loss)	(0.5)	640.3
Treasury stock, at cost (162.6 million and 159.7 million shares in 2013 and 2012)	(5,645.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,303.4	9,683.4
Total stockholders' equity	9,303.4	9,683.4
Total liabilities and stockholders' equity	11,785.3	12,160.1
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	11,469.5	10,632.1
Other investments	45.8	39.6
Cash and cash equivalents	526.4	612.5	618.4	702.4
Premiums due and other receivables	0.7	1,122.1
Other assets	78.2	51.0
Total assets	12,120.6	12,457.3
Liabilities
Income taxes currently payable	1.7	0.1
Other liabilities	425.2	603.9
Total liabilities	426.9	604.0
Stockholders' equity
Additional paid-in capital	9,424.5	9,393.8
Retained earnings (accumulated deficit)	2,236.6	1,783.4
Accumulated other comprehensive income (loss)	32.6	676.1
Total stockholders' equity attributable to Principal Financial Group, Inc.	11,693.7	11,853.3
Total stockholders' equity	11,693.7	11,853.3
Total liabilities and stockholders' equity	12,120.6	12,457.3
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	49,191.6	50,939.3
Fixed maturities, trading	589.8	616.2
Equity securities, available-for-sale	135.3	136.5
Equity securities, trading	636.7	252.8
Mortgage loans	12,121.7	11,519.7
Real estate	1,264.8	1,180.3
Policy loans	865.3	864.9
Investment in unconsolidated entities	870.6	860.2
Other investments	2,042.2	2,371.4
Cash and cash equivalents	1,272.3	4,241.3	1,599.2	2,787.9
Accrued investment income	565.4	584.4
Premiums due and other receivables	2,309.1	2,206.7
Deferred acquisition costs	2,925.4	2,590.0
Property and equipment	476.4	464.2
Goodwill	1,138.5	543.4
Other intangibles	1,517.3	914.7
Separate account assets	118,740.2	81,653.8
Other assets	1,083.3	1,003.5
Total assets	197,745.9	162,943.3
Liabilities
Contractholder funds	36,269.7	37,786.5
Future policy benefits and claims	22,129.5	22,436.2
Other policyholder funds	739.5	716.4
Short-term debt	460.8	2,564.1
Long-term debt	1,214.2	222.7
Income taxes currently payable	56.8	47.2
Deferred income taxes	710.5	686.1
Separate account liabilities	118,740.2	81,653.8
Other liabilities	5,796.1	6,117.8
Total liabilities	186,117.3	152,230.8
Redeemable noncontrolling interest	53.6	60.4
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	9,352.2	8,287.7
Retained earnings (accumulated deficit)	2,090.5	1,666.7
Accumulated other comprehensive income (loss)	11.0	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.	11,469.5	10,632.1
Noncontrolling interest	105.5	20.0
Total stockholders' equity	11,575.0	10,652.1
Total liabilities and stockholders' equity	197,745.9	162,943.3
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(23,154.5)	(22,476.6)
Cash and cash equivalents	(706.7)	(883.7)	(945.4)	(883.1)
Premiums due and other receivables	(1,090.8)	(2,244.5)
Other assets	(187.1)	(125.7)
Total assets	(25,139.1)	(25,730.5)
Liabilities
Short-term debt	(285.5)	(2,523.3)
Long-term debt	(1,084.3)
Income taxes currently payable	(51.3)	(32.0)
Deferred income taxes	(131.8)	(86.1)
Other liabilities	(423.0)	(603.7)
Total liabilities	(1,975.9)	(3,245.1)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(18,776.7)	(17,681.5)
Retained earnings (accumulated deficit)	(4,327.1)	(3,450.1)
Accumulated other comprehensive income (loss)	(43.6)	(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.	(23,163.2)	(22,485.4)
Total stockholders' equity	(23,163.2)	(22,485.4)
Total liabilities and stockholders' equity	(25,139.1)	(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