Condensed Consolidating Financial Information (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities
Net cash provided by (used in) operating activities	$ 591.3	$ 595.9
Investing activities
Available-for-sale securities: Purchases	(2,659.5)	(2,447.1)
Available-for-sale securities: Sales	475.3	503.1
Available-for-sale securities: Maturities	1,495.9	1,790.9
Mortgage loans acquired or originated	(319.3)	(610.9)
Mortgage loans sold or repaid	335.1	555.8
Real estate acquired	(182.2)	(23.4)
Net (purchases) sales of property and equipment	(49.8)	6.7
Purchases of interest in subsidiaries, net of cash acquired		(1,268.3)
Net change in other investments	69.2	(32.2)
Net cash provided by (used in) investing activities	(835.3)	(1,525.4)
Financing activities
Issuance of common stock	16.1	20.3
Acquisition of treasury stock	(89.0)	(90.9)
Proceeds from financing element derivatives	14.4	14.3
Payments for financing element derivatives	(12.7)	(12.7)
Excess tax benefits from share-based payment arrangements	4.9	3.8
Purchase of subsidiary shares from noncontrolling interest	(25.3)	(30.6)
Dividends to common stockholders	(82.7)	(67.6)
Issuance of long-term debt	14.0	3.5
Principal repayments of long-term debt	(100.1)	(0.4)
Net proceeds from (repayments of) short-term borrowings	(0.3)
Investment contract deposits	1,319.7	1,419.7
Investment contract withdrawals	(1,751.5)	(2,852.0)
Net increase (decrease) in banking operation deposits	(39.1)	6.9
Other	(3.1)	(0.8)
Net cash provided by (used in) financing activities	(734.7)	(1,586.5)
Net increase (decrease) in cash and cash equivalents	(978.7)	(2,516.0)
Cash and cash equivalents at beginning of period	2,371.8	4,177.2
Cash and cash equivalents at end of period	1,393.1	1,661.2
Principal Financial Group, Inc. Parent Only
Operating activities
Net cash provided by (used in) operating activities	1.1	28.0
Investing activities
Dividends and returns of capital received from (contributions to) unconsolidated entities	116.5	18.8
Net change in other investments	(2.2)	(3.0)
Net cash provided by (used in) investing activities	114.3	15.8
Financing activities
Issuance of common stock	16.1	20.3
Acquisition of treasury stock	(89.0)	(90.9)
Excess tax benefits from share-based payment arrangements	0.1
Dividends to common stockholders	(82.7)	(67.6)
Net cash provided by (used in) financing activities	(155.5)	(138.2)
Net increase (decrease) in cash and cash equivalents	(40.1)	(94.4)
Cash and cash equivalents at beginning of period	131.5	207.1
Cash and cash equivalents at end of period	91.4	112.7
Principal Life Insurance Company Only
Operating activities
Net cash provided by (used in) operating activities	301.4	812.7
Investing activities
Available-for-sale securities: Purchases	(2,430.9)	(2,242.7)
Available-for-sale securities: Sales	428.7	392.7
Available-for-sale securities: Maturities	1,346.1	1,596.0
Mortgage loans acquired or originated	(278.0)	(573.2)
Mortgage loans sold or repaid	283.5	519.3
Real estate acquired		0.1
Net (purchases) sales of property and equipment	(30.6)	(2.0)
Dividends and returns of capital received from (contributions to) unconsolidated entities	66.6	25.4
Net change in other investments	(2.7)	56.3
Net cash provided by (used in) investing activities	(617.3)	(228.1)
Financing activities
Proceeds from financing element derivatives	14.4	14.3
Payments for financing element derivatives	(12.7)	(12.7)
Excess tax benefits from share-based payment arrangements	2.0	1.3
Principal repayments of long-term debt	(100.0)
Capital received from (dividends and capital paid to) parent	(116.5)	(15.8)
Investment contract deposits	1,319.7	1,292.1
Investment contract withdrawals	(1,751.5)	(2,850.3)
Other	(3.3)	(0.8)
Net cash provided by (used in) financing activities	(647.9)	(1,571.9)
Net increase (decrease) in cash and cash equivalents	(963.8)	(987.3)
Cash and cash equivalents at beginning of period	1,332.2	1,698.4
Cash and cash equivalents at end of period	368.4	711.1
Principal Financial Services, Inc. and Other Subsidiaries Combined
Operating activities
Net cash provided by (used in) operating activities	116.0	(385.0)
Investing activities
Available-for-sale securities: Purchases	(228.6)	(206.4)
Available-for-sale securities: Sales	46.6	128.7
Available-for-sale securities: Maturities	149.8	194.9
Mortgage loans acquired or originated	(41.3)	(59.8)
Mortgage loans sold or repaid	51.6	79.2
Real estate acquired	(182.2)	(23.5)
Net (purchases) sales of property and equipment	(19.2)	8.7
Purchases of interest in subsidiaries, net of cash acquired		(1,268.3)
Dividends and returns of capital received from (contributions to) unconsolidated entities	116.5	15.8
Net change in other investments	64.2	(104.0)
Net cash provided by (used in) investing activities	(42.6)	(1,234.7)
Financing activities
Excess tax benefits from share-based payment arrangements	2.8	2.5
Purchase of subsidiary shares from noncontrolling interest	(25.3)	(30.6)
Issuance of long-term debt	38.2	3.5
Principal repayments of long-term debt	(0.1)	20.7
Net proceeds from (repayments of) short-term borrowings	(0.3)
Capital received from (dividends and capital paid to) parent	(183.1)	(44.2)
Investment contract deposits		127.6
Investment contract withdrawals		(1.7)
Net increase (decrease) in banking operation deposits	(39.1)	6.9
Other	0.2
Net cash provided by (used in) financing activities	(206.7)	84.7
Net increase (decrease) in cash and cash equivalents	(133.3)	(1,535.0)
Cash and cash equivalents at beginning of period	894.5	2,286.9
Cash and cash equivalents at end of period	761.2	751.9
Eliminations, Notes Guarantor
Operating activities
Net cash provided by (used in) operating activities	172.8	140.2
Investing activities
Available-for-sale securities: Purchases		2.0
Available-for-sale securities: Sales		(18.3)
Mortgage loans acquired or originated		22.1
Mortgage loans sold or repaid		(42.7)
Dividends and returns of capital received from (contributions to) unconsolidated entities	(299.6)	(60.0)
Net change in other investments	9.9	18.5
Net cash provided by (used in) investing activities	(289.7)	(78.4)
Financing activities
Issuance of long-term debt	(24.2)
Principal repayments of long-term debt		(21.1)
Capital received from (dividends and capital paid to) parent	299.6	60.0
Net cash provided by (used in) financing activities	275.4	38.9
Net increase (decrease) in cash and cash equivalents	158.5	100.7
Cash and cash equivalents at beginning of period	13.6	(15.2)
Cash and cash equivalents at end of period	$ 172.1	$ 85.5