Condensed Consolidating Financial Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Assets
Fixed maturities, available-for-sale	$ 50,048.1	$ 48,757.1
Fixed maturities, trading	575.3	563.1
Equity securities, available-for-sale	136.1	110.5
Equity securities, trading	724.2	716.9
Mortgage loans	11,478.4	11,533.6
Real estate	1,390.8	1,271.6
Policy loans	843.8	859.7
Investment in unconsolidated entities	889.0	880.0
Other investments	2,021.4	2,064.4
Cash and cash equivalents	1,393.1	2,371.8	1,661.2	4,177.2
Accrued investment income	540.4	532.1
Premiums due and other receivables	1,199.3	1,241.0
Deferred acquisition costs	3,045.6	3,077.0
Property and equipment	546.0	500.7
Goodwill	1,075.2	1,100.3
Other intangibles	1,421.8	1,459.0
Separate account assets	132,804.6	130,018.4
Other assets	1,060.8	1,134.2
Total assets	211,193.9	208,191.4
Liabilities
Contractholder funds	35,736.3	35,958.3
Future policy benefits and claims	23,026.2	22,626.2
Other policyholder funds	791.6	758.9
Short-term debt	148.8	150.6
Long-term debt	2,516.0	2,601.4
Income taxes currently payable	6.4	5.2
Deferred income taxes	889.7	824.0
Separate account liabilities	132,804.6	130,018.4
Other liabilities	4,936.2	5,224.2
Total liabilities	200,855.8	198,167.2
Redeemable noncontrolling interest	280.2	247.2	58.9	60.4
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,813.1	9,798.9
Retained earnings (accumulated deficit)	5,605.3	5,405.4
Accumulated other comprehensive income	361.8	183.2
Treasury stock, at cost (166.1 million and 164.1 million shares in 2014 and 2013)	(5,797.0)	(5,708.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,987.9	9,684.2
Noncontrolling interest	70.0	92.8
Total stockholders' equity	10,057.9	9,777.0	9,826.6	9,703.4
Total liabilities and stockholders' equity	211,193.9	208,191.4
Principal Financial Group, Inc. Parent Only
Assets
Investment in unconsolidated entities	12,326.6	11,956.2
Other investments	9.2	9.3
Cash and cash equivalents	91.4	131.5	112.7	207.1
Accrued investment income	0.1
Other assets	59.1	59.2
Total assets	12,486.4	12,156.2
Liabilities
Long-term debt	2,448.8	2,448.8
Income taxes currently payable	(0.3)
Deferred income taxes	0.3
Other liabilities	49.7	23.2
Total liabilities	2,498.5	2,472.0
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,813.1	9,798.9
Retained earnings (accumulated deficit)	5,605.3	5,405.4
Accumulated other comprehensive income	361.8	183.2
Treasury stock, at cost (166.1 million and 164.1 million shares in 2014 and 2013)	(5,797.0)	(5,708.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,987.9	9,684.2
Total stockholders' equity	9,987.9	9,684.2
Total liabilities and stockholders' equity	12,486.4	12,156.2
Principal Life Insurance Company Only
Assets
Fixed maturities, available-for-sale	44,037.2	42,794.7
Fixed maturities, trading	254.3	245.5
Equity securities, available-for-sale	108.3	102.6
Equity securities, trading	0.3	0.3
Mortgage loans	10,521.3	10,501.5
Real estate	7.8	7.9
Policy loans	815.6	830.1
Investment in unconsolidated entities	3,123.2	3,396.8
Other investments	2,348.8	1,892.4
Cash and cash equivalents	368.4	1,332.2	711.1	1,698.4
Accrued investment income	481.9	474.5
Premiums due and other receivables	1,080.8	1,029.0
Deferred acquisition costs	2,809.3	2,848.8
Property and equipment	454.5	422.1
Goodwill	54.3	54.3
Other intangibles	26.6	26.9
Separate account assets	86,550.3	83,790.2
Other assets	1,007.3	976.9
Total assets	154,050.2	150,726.7
Liabilities
Contractholder funds	34,641.7	34,918.0
Future policy benefits and claims	18,763.1	18,292.9
Other policyholder funds	733.4	705.1
Long-term debt		99.4
Deferred income taxes	131.8	(25.0)
Separate account liabilities	86,550.3	83,790.2
Other liabilities	5,202.8	5,204.8
Total liabilities	146,023.1	142,985.4
Stockholders' equity
Common stock	2.5	2.5
Additional paid-in capital	5,477.0	5,505.0
Retained earnings (accumulated deficit)	1,862.2	1,738.1
Accumulated other comprehensive income	685.4	495.7
Total stockholders' equity attributable to Principal Financial Group, Inc.	8,027.1	7,741.3
Total stockholders' equity	8,027.1	7,741.3
Total liabilities and stockholders' equity	154,050.2	150,726.7
Principal Financial Services, Inc. and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	6,406.8	6,357.5
Fixed maturities, trading	321.0	317.6
Equity securities, available-for-sale	27.8	7.9
Equity securities, trading	723.9	716.6
Mortgage loans	1,295.2	1,345.9
Real estate	1,383.0	1,263.7
Policy loans	28.2	29.6
Investment in unconsolidated entities	5,206.8	4,891.6
Other investments	1,267.4	1,238.8
Cash and cash equivalents	761.2	894.5	751.9	2,286.9
Accrued investment income	59.7	59.0
Premiums due and other receivables	1,820.2	1,814.5
Deferred acquisition costs	236.3	228.2
Property and equipment	91.5	78.6
Goodwill	1,020.9	1,046.0
Other intangibles	1,395.2	1,432.1
Separate account assets	46,254.3	46,228.2
Other assets	2,154.8	2,115.3
Total assets	70,454.2	70,065.6
Liabilities
Contractholder funds	1,389.8	1,330.7
Future policy benefits and claims	4,587.7	4,625.0
Other policyholder funds	58.9	54.2
Short-term debt	148.8	150.6
Long-term debt	405.3	367.0
Income taxes currently payable	108.0	67.4
Deferred income taxes	935.9	1,030.1
Separate account liabilities	46,254.3	46,228.2
Other liabilities	3,884.2	3,911.8
Total liabilities	57,772.9	57,765.0
Redeemable noncontrolling interest	280.2	247.2
Stockholders' equity
Additional paid-in capital	9,144.5	9,163.7
Retained earnings (accumulated deficit)	2,790.4	2,578.2
Accumulated other comprehensive income	391.7	214.3
Total stockholders' equity attributable to Principal Financial Group, Inc.	12,326.6	11,956.2
Noncontrolling interest	74.5	97.2
Total stockholders' equity	12,401.1	12,053.4
Total liabilities and stockholders' equity	70,454.2	70,065.6
Eliminations, Notes Guarantor
Assets
Fixed maturities, available-for-sale	(395.9)	(395.1)
Mortgage loans	(338.1)	(313.8)
Investment in unconsolidated entities	(19,767.6)	(19,364.6)
Other investments	(1,604.0)	(1,076.1)
Cash and cash equivalents	172.1	13.6	85.5	(15.2)
Accrued investment income	(1.3)	(1.4)
Premiums due and other receivables	(1,701.7)	(1,602.5)
Other assets	(2,160.4)	(2,017.2)
Total assets	(25,796.9)	(24,757.1)
Liabilities
Contractholder funds	(295.2)	(290.4)
Future policy benefits and claims	(324.6)	(291.7)
Other policyholder funds	(0.7)	(0.4)
Long-term debt	(338.1)	(313.8)
Income taxes currently payable	(101.3)	(62.2)
Deferred income taxes	(178.3)	(181.1)
Other liabilities	(4,200.5)	(3,915.6)
Total liabilities	(5,438.7)	(5,055.2)
Stockholders' equity
Common stock	(2.5)	(2.5)
Additional paid-in capital	(14,621.5)	(14,668.7)
Retained earnings (accumulated deficit)	(4,652.6)	(4,316.3)
Accumulated other comprehensive income	(1,077.1)	(710.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	(20,353.7)	(19,697.5)
Noncontrolling interest	(4.5)	(4.4)
Total stockholders' equity	(20,358.2)	(19,701.9)
Total liabilities and stockholders' equity	(25,796.9)	(24,757.1)
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
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