Condensed Consolidating Financial Information (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Fixed maturities, available-for-sale	$ 48,757.1	$ 50,939.3
Fixed maturities, trading	563.1	626.7
Equity securities, available-for-sale	110.5	136.5
Equity securities, trading	716.9	252.8
Mortgage loans	11,533.6	11,519.7
Real estate	1,271.6	1,180.3
Policy loans	859.7	864.9
Investment in unconsolidated entities	880.0	869.0
Other investments	2,064.4	2,422.1
Cash and cash equivalents	2,371.8	4,177.2	2,833.9	1,877.4
Accrued investment income	532.1	584.4
Premiums due and other receivables	1,241.0	1,084.4
Deferred acquisition costs	3,077.0	2,590.0	2,358.1	2,442.2
Property and equipment	500.7	464.2
Goodwill	1,100.3	543.4	482.3
Other intangibles	1,459.0	914.7
Separate account assets	130,018.4	81,653.8
Other assets	1,134.2	1,006.8
Total assets	208,191.4	161,830.2
Liabilities
Contractholder funds	35,958.3	37,786.5
Future policy benefits and claims	22,626.2	22,436.2
Other policyholder funds	758.9	716.4
Short-term debt	150.6	40.8
Long-term debt	2,601.4	2,671.3
Income taxes currently payable	5.2	15.3
Deferred income taxes	824.0	600.0
Separate account liabilities	130,018.4	81,653.8
Other liabilities	5,224.2	6,146.1
Total liabilities	198,167.2	152,066.4
Redeemable noncontrolling interest	247.2	60.4	22.2
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,798.9	9,730.9
Retained earnings (accumulated deficit)	5,405.4	4,862.0
Accumulated other comprehensive income	183.2	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,708.0)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,684.2	9,683.4
Noncontrolling interest	92.8	20.0
Total stockholders' equity	9,777.0	9,703.4	9,306.2	9,246.8
Total liabilities and stockholders' equity	208,191.4	161,830.2
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Investment in unconsolidated entities	11,956.2	11,853.3
Other investments	9.3	11.1
Cash and cash equivalents	131.5	207.1	226.7	370.9
Premiums due and other receivables		0.1
Other assets	59.2	78.0
Total assets	12,156.2	12,160.1
Liabilities
Long-term debt	2,448.8	2,448.6
Other liabilities	23.2	28.1
Total liabilities	2,472.0	2,476.7
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,798.9	9,730.9
Retained earnings (accumulated deficit)	5,405.4	4,862.0
Accumulated other comprehensive income	183.2	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,708.0)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,684.2	9,683.4
Total stockholders' equity	9,684.2	9,683.4
Total liabilities and stockholders' equity	12,156.2	12,160.1
Principal Life Insurance Company Only
Assets
Fixed maturities, available-for-sale	42,794.7	44,614.6
Fixed maturities, trading	245.5	284.4
Equity securities, available-for-sale	102.6	131.3
Equity securities, trading	0.3	0.3
Mortgage loans	10,501.5	10,054.2
Real estate	7.9	8.4
Policy loans	830.1	834.0
Investment in unconsolidated entities	3,396.8	3,309.2
Other investments	1,892.4	2,834.0
Cash and cash equivalents	1,332.2	1,698.4	1,344.5	699.8
Accrued investment income	474.5	521.6
Premiums due and other receivables	1,029.0	916.7
Deferred acquisition costs	2,848.8	2,394.8
Property and equipment	422.1	402.2
Goodwill	54.3	54.3
Other intangibles	26.9	27.9
Separate account assets	83,790.2	69,217.8
Other assets	976.9	947.8
Total assets	150,726.7	138,251.9
Liabilities
Contractholder funds	34,918.0	37,053.3
Future policy benefits and claims	18,292.9	17,944.9
Other policyholder funds	705.1	676.5
Long-term debt	99.4	99.4
Deferred income taxes	(25.0)	324.5
Separate account liabilities	83,790.2	69,217.8
Other liabilities	5,204.8	5,375.1
Total liabilities	142,985.4	130,691.5
Stockholders' equity
Common stock	2.5	2.5
Additional paid-in capital	5,505.0	5,747.6
Retained earnings (accumulated deficit)	1,738.1	1,167.7
Accumulated other comprehensive income	495.7	642.6
Total stockholders' equity attributable to Principal Financial Group, Inc.	7,741.3	7,560.4
Total stockholders' equity	7,741.3	7,560.4
Total liabilities and stockholders' equity	150,726.7	138,251.9
Principal Financial Services, Inc. and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	6,357.5	6,681.7
Fixed maturities, trading	317.6	331.8
Equity securities, available-for-sale	7.9	5.2
Equity securities, trading	716.6	252.5
Mortgage loans	1,345.9	1,775.5
Real estate	1,263.7	1,171.9
Policy loans	29.6	30.9
Investment in unconsolidated entities	4,891.6	4,808.3
Other investments	1,238.8	1,208.4
Cash and cash equivalents	894.5	2,286.9	1,277.6	719.9
Accrued investment income	59.0	64.5
Premiums due and other receivables	1,814.5	1,327.1
Deferred acquisition costs	228.2	195.2
Property and equipment	78.6	62.0
Goodwill	1,046.0	489.1
Other intangibles	1,432.1	886.8
Separate account assets	46,228.2	12,436.0
Other assets	2,115.3	1,567.7
Total assets	70,065.6	35,581.5
Liabilities
Contractholder funds	1,330.7	1,011.9
Future policy benefits and claims	4,625.0	4,679.6
Other policyholder funds	54.2	40.3
Short-term debt	150.6	40.8
Long-term debt	367.0	433.3
Income taxes currently payable	67.4	84.7
Deferred income taxes	1,030.1	378.4
Separate account liabilities	46,228.2	12,436.0
Other liabilities	3,911.8	4,538.4
Total liabilities	57,765.0	23,643.4
Redeemable noncontrolling interest	247.2	60.4
Stockholders' equity
Additional paid-in capital	9,163.7	9,393.8
Retained earnings (accumulated deficit)	2,578.2	1,783.4
Accumulated other comprehensive income	214.3	676.1
Total stockholders' equity attributable to Principal Financial Group, Inc.	11,956.2	11,853.3
Noncontrolling interest	97.2	24.4
Total stockholders' equity	12,053.4	11,877.7
Total liabilities and stockholders' equity	70,065.6	35,581.5
Eliminations, Notes Guarantor
Assets
Fixed maturities, available-for-sale	(395.1)	(357.0)
Mortgage loans	(313.8)	(310.0)
Investment in unconsolidated entities	(19,364.6)	(19,101.8)
Other investments	(1,076.1)	(1,631.4)
Cash and cash equivalents	13.6	(15.2)	(14.9)	86.8
Accrued investment income	(1.4)	(1.7)
Premiums due and other receivables	(1,602.5)	(1,159.5)
Other assets	(2,017.2)	(1,586.7)
Total assets	(24,757.1)	(24,163.3)
Liabilities
Contractholder funds	(290.4)	(278.7)
Future policy benefits and claims	(291.7)	(188.3)
Other policyholder funds	(0.4)	(0.4)
Long-term debt	(313.8)	(310.0)
Income taxes currently payable	(62.2)	(69.4)
Deferred income taxes	(181.1)	(102.9)
Other liabilities	(3,915.6)	(3,795.5)
Total liabilities	(5,055.2)	(4,745.2)
Stockholders' equity
Common stock	(2.5)	(2.5)
Additional paid-in capital	(14,668.7)	(15,141.4)
Retained earnings (accumulated deficit)	(4,316.3)	(2,951.1)
Accumulated other comprehensive income	(710.0)	(1,318.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	(19,697.5)	(19,413.7)
Noncontrolling interest	(4.4)	(4.4)
Total stockholders' equity	(19,701.9)	(19,418.1)
Total liabilities and stockholders' equity	(24,757.1)	(24,163.3)
Series A
Stockholders' equity
Preferred stock, value
Total stockholders' equity	0	0	0	0
Series B
Stockholders' equity
Preferred stock, value	0.1	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