Condensed Consolidating Financial Information (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Assets
Fixed maturities, available-for-sale	$ 49,627.5	$ 48,757.1
Fixed maturities, trading	609.4	563.1
Equity securities, available-for-sale	124.8	110.5
Equity securities, trading	807.6	716.9
Mortgage loans	11,744.9	11,533.6
Real estate	1,352.1	1,271.6
Policy loans	837.7	859.7
Investment in unconsolidated entities	873.4	880.0
Other investments	2,117.5	2,064.4
Cash and cash equivalents	1,270.8	2,371.8	1,707.1	4,177.2
Accrued investment income	545.1	532.1
Premiums due and other receivables	1,189.3	1,241.0
Deferred acquisition costs	2,985.4	3,077.0
Property and equipment	590.1	500.7
Goodwill	1,034.4	1,100.3
Other intangibles	1,361.4	1,459.0
Separate account assets	138,296.7	130,018.4
Other assets	1,054.7	1,134.2
Total assets	216,422.8	208,191.4
Liabilities
Contractholder funds	34,680.8	35,958.3
Future policy benefits and claims	23,399.5	22,626.2
Other policyholder funds	811.9	758.9
Short-term debt	126.3	150.6
Long-term debt	2,529.2	2,601.4
Income taxes currently payable	18.1	5.2
Deferred income taxes	1,150.6	824.0
Separate account liabilities	138,296.7	130,018.4
Other liabilities	4,984.6	5,224.2
Total liabilities	205,997.7	198,167.2
Redeemable noncontrolling interest	56.1	247.2	234.5	60.4
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,916.9	9,798.9
Retained earnings (accumulated deficit)	5,945.2	5,405.4
Accumulated other comprehensive income	380.1	183.2
Treasury stock, at cost (168.8 million and 164.1 million shares in 2014 and 2013)	(5,930.5)	(5,708.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,316.4	9,684.2
Noncontrolling interest	52.6	92.8
Total stockholders' equity	10,369.0	9,777.0	9,373.4	9,703.4
Total liabilities and stockholders' equity	216,422.8	208,191.4
Principal Financial Group, Inc. Parent Only
Assets
Investment in unconsolidated entities	12,583.2	11,956.2
Other investments	9.5	9.3
Cash and cash equivalents	150.7	131.5	50.8	207.1
Other assets	62.4	59.2
Total assets	12,805.8	12,156.2
Liabilities
Long-term debt	2,448.9	2,448.8
Other liabilities	40.5	23.2
Total liabilities	2,489.4	2,472.0
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,916.9	9,798.9
Retained earnings (accumulated deficit)	5,945.2	5,405.4
Accumulated other comprehensive income	380.1	183.2
Treasury stock, at cost (168.8 million and 164.1 million shares in 2014 and 2013)	(5,930.5)	(5,708.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,316.4	9,684.2
Total stockholders' equity	10,316.4	9,684.2
Total liabilities and stockholders' equity	12,805.8	12,156.2
Principal Life Insurance Company Only
Assets
Fixed maturities, available-for-sale	43,630.4	42,794.7
Fixed maturities, trading	308.7	245.5
Equity securities, available-for-sale	109.4	102.6
Equity securities, trading	0.3	0.3
Mortgage loans	10,842.0	10,501.5
Real estate	6.9	7.9
Policy loans	808.4	830.1
Investment in unconsolidated entities	3,180.2	3,396.8
Other investments	2,723.9	1,892.4
Cash and cash equivalents	149.1	1,332.2	651.6	1,698.4
Accrued investment income	488.0	474.5
Premiums due and other receivables	1,222.9	1,029.0
Deferred acquisition costs	2,739.3	2,848.8
Property and equipment	504.2	422.1
Goodwill	54.3	54.3
Other intangibles	26.0	26.9
Separate account assets	89,167.7	83,790.2
Other assets	963.2	976.9
Total assets	156,924.9	150,726.7
Liabilities
Contractholder funds	33,458.0	34,918.0
Future policy benefits and claims	19,164.8	18,292.9
Other policyholder funds	747.7	705.1
Long-term debt		99.4
Deferred income taxes	337.0	(25.0)
Separate account liabilities	89,167.7	83,790.2
Other liabilities	5,725.4	5,204.8
Total liabilities	148,600.6	142,985.4
Stockholders' equity
Common stock	2.5	2.5
Additional paid-in capital	5,511.3	5,505.0
Retained earnings (accumulated deficit)	1,978.5	1,738.1
Accumulated other comprehensive income	832.0	495.7
Total stockholders' equity attributable to Principal Financial Group, Inc.	8,324.3	7,741.3
Total stockholders' equity	8,324.3	7,741.3
Total liabilities and stockholders' equity	156,924.9	150,726.7
Principal Financial Services, Inc. and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	6,394.6	6,357.5
Fixed maturities, trading	300.7	317.6
Equity securities, available-for-sale	15.4	7.9
Equity securities, trading	807.3	716.6
Mortgage loans	1,245.0	1,345.9
Real estate	1,345.2	1,263.7
Policy loans	29.3	29.6
Investment in unconsolidated entities	5,539.4	4,891.6
Other investments	1,396.2	1,238.8
Cash and cash equivalents	833.5	894.5	934.8	2,286.9
Accrued investment income	58.3	59.0
Premiums due and other receivables	2,022.7	1,814.5
Deferred acquisition costs	246.1	228.2
Property and equipment	85.9	78.6
Goodwill	980.1	1,046.0
Other intangibles	1,335.4	1,432.1
Separate account assets	49,129.0	46,228.2
Other assets	2,591.5	2,115.3
Total assets	74,355.6	70,065.6
Liabilities
Contractholder funds	1,527.5	1,330.7
Future policy benefits and claims	4,634.9	4,625.0
Other policyholder funds	64.9	54.2
Short-term debt	126.3	150.6
Long-term debt	409.3	367.0
Income taxes currently payable	124.3	67.4
Deferred income taxes	1,055.4	1,030.1
Separate account liabilities	49,129.0	46,228.2
Other liabilities	4,587.5	3,911.8
Total liabilities	61,659.1	57,765.0
Redeemable noncontrolling interest	56.1	247.2
Stockholders' equity
Additional paid-in capital	9,191.9	9,163.7
Retained earnings (accumulated deficit)	2,983.4	2,578.2
Accumulated other comprehensive income	407.9	214.3
Total stockholders' equity attributable to Principal Financial Group, Inc.	12,583.2	11,956.2
Noncontrolling interest	57.2	97.2
Total stockholders' equity	12,640.4	12,053.4
Total liabilities and stockholders' equity	74,355.6	70,065.6
Eliminations, Notes Guarantor
Assets
Fixed maturities, available-for-sale	(397.5)	(395.1)
Mortgage loans	(342.1)	(313.8)
Investment in unconsolidated entities	(20,429.4)	(19,364.6)
Other investments	(2,012.1)	(1,076.1)
Cash and cash equivalents	137.5	13.6	69.9	(15.2)
Accrued investment income	(1.2)	(1.4)
Premiums due and other receivables	(2,056.3)	(1,602.5)
Other assets	(2,562.4)	(2,017.2)
Total assets	(27,663.5)	(24,757.1)
Liabilities
Contractholder funds	(304.7)	(290.4)
Future policy benefits and claims	(400.2)	(291.7)
Other policyholder funds	(0.7)	(0.4)
Long-term debt	(329.0)	(313.8)
Income taxes currently payable	(106.2)	(62.2)
Deferred income taxes	(241.8)	(181.1)
Other liabilities	(5,368.8)	(3,915.6)
Total liabilities	(6,751.4)	(5,055.2)
Stockholders' equity
Common stock	(2.5)	(2.5)
Additional paid-in capital	(14,703.2)	(14,668.7)
Retained earnings (accumulated deficit)	(4,961.9)	(4,316.3)
Accumulated other comprehensive income	(1,239.9)	(710.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	(20,907.5)	(19,697.5)
Noncontrolling interest	(4.6)	(4.4)
Total stockholders' equity	(20,912.1)	(19,701.9)
Total liabilities and stockholders' equity	(27,663.5)	(24,757.1)
Series A
Stockholders' equity
Preferred stock, value
Total stockholders' equity	0	0	0	0
Series A | Principal Financial Group, Inc. Parent Only
Stockholders' equity
Preferred stock, value
Series B
Stockholders' equity
Preferred stock, value	0.1	0.1
Total stockholders' equity	0.1	0.1	0.1	0.1
Series B | Principal Financial Group, Inc. Parent Only
Stockholders' equity
Preferred stock, value	$ 0.1	$ 0.1