Schedule II - Condensed Financial Information of Registrant (Parent Only) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Fixed maturities, trading	$ 563.1	$ 626.7
Cash and cash equivalents	2,371.8	4,177.2	2,833.9	1,877.4
Other investments	2,944.4	3,291.1
Deferred income taxes	49.6	20.8
Investment in subsidiary	880.0	869.0
Total assets	208,191.4	161,830.2
Liabilities
Long-term debt	2,601.4	2,671.3
Total liabilities	198,167.2	152,066.4
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 (loss)	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 liabilities and stockholders' equity	208,191.4	161,830.2
Series A
Stockholders' equity
Preferred stock, value
Series B
Stockholders' equity
Preferred stock, value	0.1	0.1	0.1
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Cash and cash equivalents	131.5	207.1	226.7	370.9
Other investments	9.3	11.1
Income taxes receivable	22.2	35.8
Deferred income taxes	17.2	20.6
Amounts receivable from subsidiary	0.8	0.9
Other assets	19.0	20.8
Investment in subsidiary	11,956.2	11,853.3
Total assets	12,156.2	12,160.1
Liabilities
Amounts payable to subsidiary	1.4	2.1
Long-term debt	2,448.8	2,448.6
Accrued interest payable	21.8	22.3
Other liabilities		3.7
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 (loss)	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 liabilities and stockholders' equity	12,156.2	12,160.1
Principal Financial Group, Inc. Parent Only | Series A
Stockholders' equity
Preferred stock, value
Principal Financial Group, Inc. Parent Only | Series B
Stockholders' equity
Preferred stock, value	$ 0.1	$ 0.1