Segment Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information
Operating revenues	$ 2,638.6	$ 2,031.7	$ 6,882.3	$ 6,177.7
Net realized capital gains (losses), net of related revenue adjustments	64.9	(55.8)	12.8	(124.1)
Exited group medical insurance business	1.2	117.7	24.1	553.4
Assumption change within Individual Life business				4.9
Total revenues	2,704.7	2,093.6	6,919.2	6,611.9
Operating earnings (loss)	134.8	193.2	564.1	642.0
Net realized capital gains (losses), as adjusted	88.8	(56.8)	39.6	(88.2)
Other after-tax adjustments	(43.9)	(64.5)	(49.4)	(82.6)
Net income (loss) available to common stockholders	179.7	71.9	554.3	471.2
Impact of court ruling on uncertain tax positions		(68.9)		(68.9)
Impact of assumption change within Individual Life business				(34.5)
Contribution to The Principal Financial Group Foundation, Inc.	(39.8)		(39.8)	(19.5)
Estimated obligation associated with Executive Life of New York's liquidation petition		(10.5)		(10.5)
After-tax gains (losses) associated with exited group medical insurance business that does not qualify for discontinued operations	(4.1)	14.9	(9.6)	50.8
Retirement and Investor Services
Segment Reporting Information
Operating revenues	1,570.7	996.0	3,707.0	3,058.1
Operating earnings (loss)	137.5	129.6	422.8	438.4
Principal Global Investors
Segment Reporting Information
Operating revenues	144.0	132.9	423.2	394.5
Operating earnings (loss)	20.6	19.1	55.0	56.5
Principal International
Segment Reporting Information
Operating revenues	203.8	220.1	676.9	653.4
Operating earnings (loss)	29.5	35.3	108.2	99.4
U.S. Insurance Solutions
Segment Reporting Information
Operating revenues	766.5	739.3	2,215.0	2,202.0
Operating earnings (loss)	(21.6)	49.1	78.8	151.5
Corporate
Segment Reporting Information
Operating revenues	(46.4)	(56.6)	(139.8)	(130.3)
Operating earnings (loss)	$ (31.2)	$ (39.9)	$ (100.7)	$ (103.8)

After-tax adjustment for the impact of an assumption change in the Individual Life business.

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Aggregate revenue recognized during the period for an assumption change in the Individual Life business.

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Other after-tax adjustment for the impact of a court ruling on some uncertain tax positions.

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Other after-tax adjustment for the estimated obligation associated with Executive Life of New York's liquidation petition.

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Aggregate revenue recognized during the period for an exited group medical insurance business that does not qualify for discontinued accounting treatment.

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The after-tax gain (loss) resulting from an exited group medical insurance business that is not a discontinued operation. It is included in income from continuing operations in the income statement.

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Operating earnings is a measure of profit or loss for the operating segments that is used to evaluate performance on a basis comparable to that used by securities analysts. It is derived by adjusting net income for net realized capital gains (losses), as adjusted, and other after-tax adjustments management believes are not indicative of overall operating trends.

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Other after-tax adjustment for charitable contribution to The Principal Financial Group Foundation, Inc.

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Net realized capital gains (losses) net of recognition of deferred front-end fee revenues for sales charges on retirement products and services and certain market value adjustments to fee revenues. It excludes periodic settlements and accruals on derivatives not designated as hedging instruments.

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Net realized capital gains (losses) net of income taxes, related changes in the amortization pattern of deferred policy acquisition costs and sales inducements, recognition of deferred front-end fee revenues for sales charges on retirement products and services, net realized capital gains and losses distributed, noncontrolling interest capital gains and losses and certain market value adjustments to fee revenues. Net realized capital gains (losses), as adjusted, exclude periodic settlements and accruals on derivative instruments not designated as hedging instruments and exclude certain market value adjustments of embedded derivatives.

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The after-tax impact of specific transactions that are not recurring in nature and that management does not believe are indicative of overall operating trends.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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-SubTopic 10

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-Subparagraph (SX 210.5-03.1)

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-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Article 5

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Amount of total revenue for the reportable segments, including revenue from external customers, transactions with other operating segments of the same entity, and (gross) interest revenue. All considered to be "operating revenue" for purposes of the taxonomy.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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