Schedule III - Supplementary Insurance Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplementary Insurance Information
Deferred acquisition costs	$ 2,590.0				$ 3,077.0	$ 2,590.0	$ 2,358.1	$ 2,442.2
Future policy benefits and claims	22,436.2				22,626.2	22,436.2
Contractholder and other policyholder funds	38,502.9				36,717.2	38,502.9
Premiums and other considerations	700.1	1,158.2	681.3	679.8	3,154.1	3,219.4	2,891.0
Net investment income (loss)	845.3	783.8	801.0	824.8	3,138.4	3,254.9	3,375.3
Benefits, claims and settlement expenses	1,154.4	1,647.0	1,110.0	1,212.5	4,683.6	5,123.9	4,616.6
Amortization of deferred acquisition costs					187.1	94.9	271.4
Other operating expenses					3,105.8	2,838.6	2,699.7
Retirement and Investor Services
Supplementary Insurance Information
Deferred acquisition costs	699.4				848.9	699.4
Future policy benefits and claims	9,702.7				9,975.6	9,702.7
Contractholder and other policyholder funds	32,801.4				30,537.5	32,801.4
Premiums and other considerations					1,045.5	1,162.6	390.4
Net investment income (loss)					1,933.3	2,075.4	2,182.8
Benefits, claims and settlement expenses					2,303.4	2,629.1	1,933.3
Amortization of deferred acquisition costs					75.0	84.8	119.4
Other operating expenses					1,529.9	1,362.5	1,258.5
Principal Global Investors
Supplementary Insurance Information
Net investment income (loss)					17.0	15.4	15.1
Other operating expenses					545.7	456.9	429.3
Principal International
Supplementary Insurance Information
Deferred acquisition costs	195.3				228.2	195.3
Future policy benefits and claims	4,435.5				4,220.2	4,435.5
Contractholder and other policyholder funds	108.5				172.2	108.5
Premiums and other considerations					291.6	284.6	264.5
Net investment income (loss)					447.1	435.2	469.9
Benefits, claims and settlement expenses					569.0	567.2	581.7
Amortization of deferred acquisition costs					16.5	12.6	8.4
Other operating expenses					318.0	208.5	184.8
U.S. Insurance Solutions
Supplementary Insurance Information
Deferred acquisition costs	1,695.3				1,999.9	1,695.3
Future policy benefits and claims	8,247.6				8,389.0	8,247.6
Contractholder and other policyholder funds	5,867.4				6,293.9	5,867.4
Premiums and other considerations					1,816.5	1,769.3	1,724.0
Net investment income (loss)					686.3	675.2	669.9
Benefits, claims and settlement expenses					1,826.0	1,935.5	1,725.1
Amortization of deferred acquisition costs					95.6	(2.5)	143.6
Other operating expenses					689.0	662.0	630.2
Corporate
Supplementary Insurance Information
Future policy benefits and claims	50.4				41.4	50.4
Contractholder and other policyholder funds	(274.4)				(286.4)	(274.4)
Premiums and other considerations					0.5	2.9	512.1
Net investment income (loss)					54.7	53.7	37.6
Benefits, claims and settlement expenses					(14.8)	(7.9)	376.5
Other operating expenses					$ 23.2	$ 148.7	$ 196.9