Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Assets
Fixed maturities, available-for-sale	$ 49,755.7	$ 49,670.8
Fixed maturities, trading	574.0	604.6
Equity securities, available-for-sale	144.9	123.0
Equity securities, trading	875.1	840.2
Mortgage loans	11,899.5	11,811.6
Real estate	1,391.7	1,344.6
Policy loans	826.0	829.2
Investment in unconsolidated entities	681.9	815.8
Other investments	2,713.7	2,394.0
Cash and cash equivalents	1,452.0	1,863.9	1,393.1	2,371.8
Accrued investment income	531.1	505.9
Premiums due and other receivables	1,230.0	1,213.0
Deferred acquisition costs	3,020.8	2,993.0
Property and equipment	607.4	590.2
Goodwill	981.0	1,007.4
Other intangibles	1,291.2	1,323.5
Separate account assets	143,505.2	140,072.8
Other assets	1,013.7	1,083.5
Total assets	222,494.9	219,087.0
Liabilities
Contractholder funds	34,173.8	34,726.7
Future policy benefits and claims	24,377.1	24,036.6
Other policyholder funds	853.1	812.7
Short-term debt	27.2	28.0
Long-term debt	2,514.6	2,531.2
Income taxes currently payable	12.0	11.5
Deferred income taxes	968.5	1,035.3
Separate account liabilities	143,505.2	140,072.8
Other liabilities	5,506.3	5,542.2
Total liabilities	211,937.8	208,797.0
Redeemable noncontrolling interest	65.0	58.0	280.2	247.2
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,975.6	9,945.5
Retained earnings (accumulated deficit)	6,420.4	6,114.1
Accumulated other comprehensive income	28.0	50.4
Treasury stock, at cost	(6,006.1)	(5,930.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,422.6	10,184.0
Noncontrolling interest	69.5	48.0
Total stockholders' equity	10,492.1	10,232.0	10,057.9	9,777.0
Total liabilities and stockholders' equity	222,494.9	219,087.0
Principal Financial Group, Inc. Parent Only
Assets
Investment in unconsolidated entities	12,636.7	12,446.5
Other investments	9.5	9.5
Cash and cash equivalents	475.4	412.4	91.4	131.5
Accrued investment income	0.1
Other assets	448.5	450.7
Total assets	13,570.2	13,319.1
Liabilities
Long-term debt	2,449.0	2,448.9
Other liabilities	698.6	686.2
Total liabilities	3,147.6	3,135.1
Stockholders' equity
Common stock	4.6	4.6
Additional paid-in capital	9,975.6	9,945.5
Retained earnings (accumulated deficit)	6,420.4	6,114.1
Accumulated other comprehensive income	28.0	50.4
Treasury stock, at cost	(6,006.1)	(5,930.7)
Total stockholders' equity attributable to Principal Financial Group, Inc.	10,422.6	10,184.0
Total stockholders' equity	10,422.6	10,184.0
Total liabilities and stockholders' equity	13,570.2	13,319.1
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	12,296.2	12,042.5
Other investments	131.1	128.2
Cash and cash equivalents	557.7	907.2	573.7	688.7
Premiums due and other receivables	0.8	0.3
Other assets	205.6	167.6
Total assets	13,191.4	13,245.8
Liabilities
Income taxes currently payable	13.7	4.3
Other liabilities	620.6	872.8
Total liabilities	634.3	877.1
Stockholders' equity
Additional paid-in capital	8,950.0	8,964.2
Retained earnings (accumulated deficit)	3,099.8	2,858.6
Accumulated other comprehensive income	507.3	545.9
Total stockholders' equity attributable to Principal Financial Group, Inc.	12,557.1	12,368.7
Total stockholders' equity	12,557.1	12,368.7
Total liabilities and stockholders' equity	13,191.4	13,245.8
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	49,755.7	49,670.8
Fixed maturities, trading	574.0	604.6
Equity securities, available-for-sale	144.9	123.0
Equity securities, trading	875.1	840.2
Mortgage loans	11,899.5	11,811.6
Real estate	1,391.7	1,344.6
Policy loans	826.0	829.2
Investment in unconsolidated entities	645.7	781.9
Other investments	2,573.1	2,256.3
Cash and cash equivalents	1,227.5	1,598.0	1,367.3	2,384.0
Accrued investment income	531.0	505.9
Premiums due and other receivables	1,228.3	1,211.8
Deferred acquisition costs	3,020.8	2,993.0
Property and equipment	607.4	590.2
Goodwill	981.0	1,007.4
Other intangibles	1,291.2	1,323.5
Separate account assets	143,505.2	140,072.8
Other assets	1,052.2	1,117.7
Total assets	222,130.3	218,682.5
Liabilities
Contractholder funds	34,173.8	34,726.7
Future policy benefits and claims	24,377.1	24,036.6
Other policyholder funds	853.1	812.7
Short-term debt	183.5	182.5
Long-term debt	65.6	82.3
Income taxes currently payable	68.2	54.1
Deferred income taxes	1,580.0	1,626.1
Separate account liabilities	143,505.2	140,072.8
Other liabilities	4,813.5	4,862.4
Total liabilities	209,620.0	206,456.2
Redeemable noncontrolling interest	65.0	58.0
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	9,382.4	9,341.0
Retained earnings (accumulated deficit)	2,569.0	2,283.2
Accumulated other comprehensive income	408.6	480.3
Treasury stock, at cost	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	12,375.8	12,120.3
Noncontrolling interest	69.5	48.0
Total stockholders' equity	12,445.3	12,168.3
Total liabilities and stockholders' equity	222,130.3	218,682.5
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(24,896.7)	(24,455.1)
Cash and cash equivalents	(808.6)	(1,053.7)	(639.3)	(832.4)
Premiums due and other receivables	0.9	0.9
Other assets	(692.6)	(652.5)
Total assets	(26,397.0)	(26,160.4)
Liabilities
Short-term debt	(156.3)	(154.5)
Income taxes currently payable	(69.9)	(46.9)
Deferred income taxes	(611.5)	(590.8)
Other liabilities	(626.4)	(879.2)
Total liabilities	(1,464.1)	(1,671.4)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(18,332.4)	(18,305.2)
Retained earnings (accumulated deficit)	(5,668.8)	(5,141.8)
Accumulated other comprehensive income	(915.9)	(1,026.2)
Treasury stock, at cost	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(24,932.9)	(24,489.0)
Total stockholders' equity	(24,932.9)	(24,489.0)
Total liabilities and stockholders' equity	(26,397.0)	(26,160.4)
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