Segment Information (Details 5) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Operating Revenues for Products and Services
Operating revenues	$ 2,026.3	$ 1,986.7	$ 6,222.0	$ 5,935.4
Net realized capital gains (losses), net of related revenue adjustments	(55.2)	(42.3)	(124.8)	(199.5)
Exited group medical insurance business	117.7	344.1	553.4	1,050.2
Total revenues	2,088.8	2,288.5	6,650.6	6,786.1
Retirement and Investor Services
Operating Revenues for Products and Services
Operating revenues	995.5	997.0	3,057.4	3,031.0
Retirement and Investor Services \| Total Accumulation
Operating Revenues for Products and Services
Operating revenues	747.1	704.9	2,271.8	2,117.9
Retirement and Investor Services \| Full service accumulation
Operating Revenues for Products and Services
Operating revenues	331.8	328.8	1,017.3	991.8
Retirement and Investor Services \| Principal Funds
Operating Revenues for Products and Services
Operating revenues	138.8	123.7	424.6	372.3
Retirement and Investor Services \| Individual annuities
Operating Revenues for Products and Services
Operating revenues	278.2	253.2	840.6	759.5
Retirement and Investor Services \| Bank and trust services
Operating Revenues for Products and Services
Operating revenues	26.0	23.5	74.4	68.4
Retirement and Investor Services \| Accumulation Eliminations
Operating Revenues for Products and Services
Operating revenues	(27.7)	(24.3)	(85.1)	(74.1)
Retirement and Investor Services \| Total Guaranteed
Operating Revenues for Products and Services
Operating revenues	248.4	292.1	785.6	913.1
Retirement and Investor Services \| Investment only
Operating Revenues for Products and Services
Operating revenues	123.1	157.0	386.5	495.3
Retirement and Investor Services \| Full service payout
Operating Revenues for Products and Services
Operating revenues	125.3	135.1	399.1	417.8
Principal Global Investors
Operating Revenues for Products and Services
Operating revenues	132.9	118.0	394.5	346.1
Inter-segment revenues	54.0	48.9	161.5	148.2
Principal International
Operating Revenues for Products and Services
Operating revenues	220.2	200.1	653.8	569.4
U.S. Insurance Solutions
Operating Revenues for Products and Services
Operating revenues	734.3	690.7	2,246.6	2,070.1
U.S. Insurance Solutions \| Individual life insurance
Operating Revenues for Products and Services
Operating revenues	357.9	339.5	1,119.3	1,019.9
U.S. Insurance Solutions \| Specialty benefits insurance
Operating Revenues for Products and Services
Operating revenues	376.4	351.2	1,127.3	1,050.2
Corporate
Operating Revenues for Products and Services
Operating revenues	$ (56.6)	$ (19.1)	$ (130.3)	$ (81.2)

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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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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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.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 1

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 27

-Subparagraph a, b, c

-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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 280

-SubTopic 10

-Section 50

-Paragraph 22

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8736-108599

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