Condensed Consolidating Financial Information (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Assets
Fixed maturities, available-for-sale	$ 48,914.9	$ 50,939.3
Fixed maturities, trading	572.9	626.7
Equity securities, available-for-sale	114.0	136.5
Equity securities, trading	666.2	252.8
Mortgage loans	11,868.1	11,519.7
Real estate	1,278.6	1,180.3
Policy loans	859.6	864.9
Investment in unconsolidated entities	900.4	869.0
Other investments	2,093.6	2,422.1
Cash and cash equivalents	1,707.1	4,177.2	2,279.0	2,833.9
Accrued investment income	571.2	584.4
Premiums due and other receivables	1,160.7	1,084.4
Deferred acquisition costs	3,007.6	2,590.0
Property and equipment	479.1	464.2
Goodwill	1,127.5	543.4
Other intangibles	1,497.4	914.7
Separate account assets	123,800.5	81,653.8
Other assets	1,068.0	1,006.8
Total assets	201,687.4	161,830.2
Liabilities
Contractholder funds	36,402.7	37,786.5
Future policy benefits and claims	22,324.2	22,436.2
Other policyholder funds	753.6	716.4
Short-term debt	175.5	40.8
Long-term debt	2,593.3	2,671.3
Income taxes currently payable	7.9	15.3
Deferred income taxes	634.6	600.0
Separate account liabilities	123,800.5	81,653.8
Other liabilities	5,387.2	6,146.1
Total liabilities	192,079.5	152,066.4
Redeemable noncontrolling interest	234.5	60.4	61.0	22.2
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,749.3	9,730.9
Retained earnings (accumulated deficit)	5,249.9	4,862.0
Accumulated other comprehensive income (loss)	(17.7)	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,707.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,278.4	9,683.4
Noncontrolling interest	95.0	20.0
Total stockholders' equity	9,373.4	9,703.4	9,779.1	9,306.2
Total liabilities and stockholders' equity	201,687.4	161,830.2
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Investment in unconsolidated entities	11,642.3	11,853.3
Other investments	9.3	11.1
Cash and cash equivalents	50.8	207.1	975.2	226.7
Premiums due and other receivables		0.1
Other assets	66.7	78.0
Total assets	11,769.1	12,160.1
Liabilities
Long-term debt	2,448.7	2,448.6
Other liabilities	42.0	28.1
Total liabilities	2,490.7	2,476.7
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,749.3	9,730.9
Retained earnings (accumulated deficit)	5,249.9	4,862.0
Accumulated other comprehensive income (loss)	(17.7)	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,707.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,278.4	9,683.4
Total stockholders' equity	9,278.4	9,683.4
Total liabilities and stockholders' equity	11,769.1	12,160.1
Principal Life Insurance Company Only
Assets
Fixed maturities, available-for-sale	42,736.2	44,614.6
Fixed maturities, trading	254.9	284.4
Equity securities, available-for-sale	103.3	131.3
Equity securities, trading	0.3	0.3
Mortgage loans	10,857.9	10,054.2
Real estate	8.0	8.4
Policy loans	829.1	834.0
Investment in unconsolidated entities	3,392.1	3,309.2
Other investments	2,024.1	2,834.0
Cash and cash equivalents	651.6	1,698.4	527.2	1,344.5
Accrued investment income	508.8	521.6
Premiums due and other receivables	1,022.2	916.7
Deferred acquisition costs	2,790.2	2,394.8
Property and equipment	401.5	402.2
Goodwill	54.3	54.3
Other intangibles	27.1	27.9
Separate account assets	78,819.5	69,217.8
Other assets	893.1	947.8
Total assets	145,374.2	138,251.9
Liabilities
Contractholder funds	35,435.4	37,053.3
Future policy benefits and claims	17,888.0	17,944.9
Other policyholder funds	703.3	676.5
Long-term debt	99.4	99.4
Deferred income taxes	(66.2)	324.5
Separate account liabilities	78,819.5	69,217.8
Other liabilities	5,138.6	5,375.1
Total liabilities	138,018.0	130,691.5
Stockholders' equity
Common stock	2.5	2.5
Additional paid-in capital	5,505.9	5,747.6
Retained earnings (accumulated deficit)	1,643.8	1,167.7
Accumulated other comprehensive income (loss)	204.0	642.6
Total stockholders' equity attributable to Principal Financial Group, Inc.	7,356.2	7,560.4
Total stockholders' equity	7,356.2	7,560.4
Total liabilities and stockholders' equity	145,374.2	138,251.9
Principal Financial Services, Inc. and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	6,567.9	6,681.7
Fixed maturities, trading	318.0	331.8
Equity securities, available-for-sale	10.7	5.2
Equity securities, trading	665.9	252.5
Mortgage loans	1,334.5	1,775.5
Real estate	1,270.6	1,171.9
Policy loans	30.5	30.9
Investment in unconsolidated entities	4,396.6	4,808.3
Other investments	1,263.5	1,208.4
Cash and cash equivalents	934.8	2,286.9	756.3	1,277.6
Accrued investment income	63.9	64.5
Premiums due and other receivables	1,648.1	1,327.1
Deferred acquisition costs	217.4	195.2
Property and equipment	77.6	62.0
Goodwill	1,073.2	489.1
Other intangibles	1,470.3	886.8
Separate account assets	44,981.0	12,436.0
Other assets	1,859.7	1,567.7
Total assets	68,184.2	35,581.5
Liabilities
Contractholder funds	1,254.4	1,011.9
Future policy benefits and claims	4,709.9	4,679.6
Other policyholder funds	50.8	40.3
Short-term debt	175.5	40.8
Long-term debt	369.6	433.3
Income taxes currently payable	80.8	84.7
Deferred income taxes	869.3	378.4
Separate account liabilities	44,981.0	12,436.0
Other liabilities	3,716.6	4,538.4
Total liabilities	56,207.9	23,643.4
Redeemable noncontrolling interest	234.5	60.4
Stockholders' equity
Additional paid-in capital	9,160.8	9,393.8
Retained earnings (accumulated deficit)	2,467.0	1,783.4
Accumulated other comprehensive income (loss)	14.5	676.1
Total stockholders' equity attributable to Principal Financial Group, Inc.	11,642.3	11,853.3
Noncontrolling interest	99.5	24.4
Total stockholders' equity	11,741.8	11,877.7
Total liabilities and stockholders' equity	68,184.2	35,581.5
Eliminations, Notes Guarantor
Assets
Fixed maturities, available-for-sale	(389.2)	(357.0)
Mortgage loans	(324.3)	(310.0)
Investment in unconsolidated entities	(18,530.6)	(19,101.8)
Other investments	(1,203.3)	(1,631.4)
Cash and cash equivalents	69.9	(15.2)	20.3	(14.9)
Accrued investment income	(1.5)	(1.7)
Premiums due and other receivables	(1,509.6)	(1,159.5)
Other assets	(1,751.5)	(1,586.7)
Total assets	(23,640.1)	(24,163.3)
Liabilities
Contractholder funds	(287.1)	(278.7)
Future policy benefits and claims	(273.7)	(188.3)
Other policyholder funds	(0.5)	(0.4)
Long-term debt	(324.4)	(310.0)
Income taxes currently payable	(72.9)	(69.4)
Deferred income taxes	(168.5)	(102.9)
Other liabilities	(3,510.0)	(3,795.5)
Total liabilities	(4,637.1)	(4,745.2)
Stockholders' equity
Common stock	(2.5)	(2.5)
Additional paid-in capital	(14,666.7)	(15,141.4)
Retained earnings (accumulated deficit)	(4,110.8)	(2,951.1)
Accumulated other comprehensive income (loss)	(218.5)	(1,318.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	(18,998.5)	(19,413.7)
Noncontrolling interest	(4.5)	(4.4)
Total stockholders' equity	(19,003.0)	(19,418.1)
Total liabilities and stockholders' equity	(23,640.1)	(24,163.3)
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