Condensed Consolidating Financial Information (Details 4) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Assets
Fixed maturities, available-for-sale	$ 48,914.9	$ 50,939.3
Fixed maturities, trading	572.9	626.7
Equity securities, available-for-sale	114.0	136.5
Equity securities, trading	666.2	252.8
Mortgage loans	11,868.1	11,519.7
Real estate	1,278.6	1,180.3
Policy loans	859.6	864.9
Investment in unconsolidated entities	900.4	869.0
Other investments	2,093.6	2,422.1
Cash and cash equivalents	1,707.1	4,177.2	2,279.0	2,833.9
Accrued investment income	571.2	584.4
Premiums due and other receivables	1,160.7	1,084.4
Deferred acquisition costs	3,007.6	2,590.0
Property and equipment	479.1	464.2
Goodwill	1,127.5	543.4
Other intangibles	1,497.4	914.7
Separate account assets	123,800.5	81,653.8
Other assets	1,068.0	1,006.8
Total assets	201,687.4	161,830.2
Liabilities
Contractholder funds	36,402.7	37,786.5
Future policy benefits and claims	22,324.2	22,436.2
Other policyholder funds	753.6	716.4
Short-term debt	175.5	40.8
Long-term debt	2,593.3	2,671.3
Income taxes currently payable	7.9	15.3
Deferred income taxes	634.6	600.0
Separate account liabilities	123,800.5	81,653.8
Other liabilities	5,387.2	6,146.1
Total liabilities	192,079.5	152,066.4
Redeemable noncontrolling interest	234.5	60.4	61.0	22.2
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,749.3	9,730.9
Retained earnings (accumulated deficit)	5,249.9	4,862.0
Accumulated other comprehensive income (loss)	(17.7)	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,707.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,278.4	9,683.4
Noncontrolling interest	95.0	20.0
Total stockholders' equity	9,373.4	9,703.4	9,779.1	9,306.2
Total liabilities and stockholders' equity	201,687.4	161,830.2
Principal Financial Group, Inc. Parent Only
Assets
Fixed maturities, trading		10.5
Investment in unconsolidated entities	11,642.3	11,853.3
Other investments	9.3	11.1
Cash and cash equivalents	50.8	207.1	975.2	226.7
Premiums due and other receivables		0.1
Other assets	66.7	78.0
Total assets	11,769.1	12,160.1
Liabilities
Long-term debt	2,448.7	2,448.6
Other liabilities	42.0	28.1
Total liabilities	2,490.7	2,476.7
Stockholders' equity
Common stock	4.6	4.5
Additional paid-in capital	9,749.3	9,730.9
Retained earnings (accumulated deficit)	5,249.9	4,862.0
Accumulated other comprehensive income (loss)	(17.7)	640.3
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(5,707.8)	(5,554.4)
Total stockholders' equity attributable to Principal Financial Group, Inc.	9,278.4	9,683.4
Total stockholders' equity	9,278.4	9,683.4
Total liabilities and stockholders' equity	11,769.1	12,160.1
Principal Financial Services, Inc. Only
Assets
Investment in unconsolidated entities	11,404.6	10,632.1
Other investments	55.8	39.6
Cash and cash equivalents	491.0	612.5	459.5	702.4
Premiums due and other receivables	0.9	1,122.1
Other assets	88.1	51.0
Total assets	12,040.4	12,457.3
Liabilities
Income taxes currently payable	10.9	0.1
Other liabilities	387.2	603.9
Total liabilities	398.1	604.0
Stockholders' equity
Additional paid-in capital	9,160.8	9,393.8
Retained earnings (accumulated deficit)	2,467.0	1,783.4
Accumulated other comprehensive income (loss)	14.5	676.1
Total stockholders' equity attributable to Principal Financial Group, Inc.	11,642.3	11,853.3
Total stockholders' equity	11,642.3	11,853.3
Total liabilities and stockholders' equity	12,040.4	12,457.3
Principal Life Insurance Company and Other Subsidiaries Combined
Assets
Fixed maturities, available-for-sale	48,914.9	50,939.3
Fixed maturities, trading	572.9	616.2
Equity securities, available-for-sale	114.0	136.5
Equity securities, trading	666.2	252.8
Mortgage loans	11,868.1	11,519.7
Real estate	1,278.6	1,180.3
Policy loans	859.6	864.9
Investment in unconsolidated entities	900.3	860.2
Other investments	2,028.6	2,371.4
Cash and cash equivalents	1,822.1	4,241.3	1,558.9	2,787.9
Accrued investment income	571.2	584.4
Premiums due and other receivables	2,261.2	2,206.7
Deferred acquisition costs	3,007.6	2,590.0
Property and equipment	479.1	464.2
Goodwill	1,127.5	543.4
Other intangibles	1,497.4	914.7
Separate account assets	123,800.5	81,653.8
Other assets	1,116.4	1,003.5
Total assets	202,886.2	162,943.3
Liabilities
Contractholder funds	36,402.7	37,786.5
Future policy benefits and claims	22,324.2	22,436.2
Other policyholder funds	753.6	716.4
Short-term debt	453.9	2,564.1
Long-term debt	1,228.9	222.7
Income taxes currently payable	55.2	47.2
Deferred income taxes	776.0	686.1
Separate account liabilities	123,800.5	81,653.8
Other liabilities	5,357.1	6,117.8
Total liabilities	191,152.1	152,230.8
Redeemable noncontrolling interest	234.5	60.4
Stockholders' equity
Common stock	17.8	17.8
Additional paid-in capital	9,068.4	8,287.7
Retained earnings (accumulated deficit)	2,327.3	1,666.7
Accumulated other comprehensive income (loss)	(6.9)	661.9
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	(2.0)	(2.0)
Total stockholders' equity attributable to Principal Financial Group, Inc.	11,404.6	10,632.1
Noncontrolling interest	95.0	20.0
Total stockholders' equity	11,499.6	10,652.1
Total liabilities and stockholders' equity	202,886.2	162,943.3
Eliminations, Shelf Registration Debt Guarantor
Assets
Investment in unconsolidated entities	(23,046.8)	(22,476.6)
Other investments	(0.1)
Cash and cash equivalents	(656.8)	(883.7)	(714.6)	(883.1)
Premiums due and other receivables	(1,101.4)	(2,244.5)
Other assets	(203.2)	(125.7)
Total assets	(25,008.3)	(25,730.5)
Liabilities
Short-term debt	(278.4)	(2,523.3)
Long-term debt	(1,084.3)
Income taxes currently payable	(58.2)	(32.0)
Deferred income taxes	(141.4)	(86.1)
Other liabilities	(399.1)	(603.7)
Total liabilities	(1,961.4)	(3,245.1)
Stockholders' equity
Common stock	(17.8)	(17.8)
Additional paid-in capital	(18,229.2)	(17,681.5)
Retained earnings (accumulated deficit)	(4,794.3)	(3,450.1)
Accumulated other comprehensive income (loss)	(7.6)	(1,338.0)
Treasury stock, at cost (164.1 million and 159.7 million shares in 2013 and 2012)	2.0	2.0
Total stockholders' equity attributable to Principal Financial Group, Inc.	(23,046.9)	(22,485.4)
Total stockholders' equity	(23,046.9)	(22,485.4)
Total liabilities and stockholders' equity	(25,008.3)	(25,730.5)
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