Condensed Consolidating Financial Information (Details 6) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating activities
Net cash provided by (used in) operating activities	$ 1,397.9	$ 2,373.7
Investing activities
Available-for-sale securities: Purchases	(7,012.3)	(6,467.5)
Available-for-sale securities: Sales	1,626.7	946.5
Available-for-sale securities: Maturities	5,783.2	4,702.7
Mortgage loans acquired or originated	(2,020.0)	(1,811.8)
Mortgage loans sold or repaid	1,570.8	1,166.7
Real estate acquired	(59.0)	(114.8)
Net (purchases) sales of property and equipment	(22.7)	(35.6)
Purchases of interest in subsidiaries, net of cash acquired	(1,268.3)	(62.5)
Net change in other investments	(31.2)	(42.9)
Net cash provided by (used in) investing activities	(1,432.8)	(1,719.2)
Financing activities
Issuance of common stock	80.2	24.7
Acquisition of treasury stock	(153.4)	(272.7)
Proceeds from financing element derivatives	46.7	51.6
Payments for financing element derivatives	(36.9)	(38.3)
Excess tax benefits from share-based payment arrangements	8.6	9.8
Purchase of subsidiary shares from noncontrolling interest	(51.7)
Sale of subsidiary shares to noncontrolling interest	32.1
Dividends to common stockholders	(211.7)	(169.6)
Dividends to preferred stockholders	(24.7)	(16.5)
Issuance of long-term debt	24.1	602.9
Principal repayments of long-term debt	(212.2)	(2.1)
Net proceeds from (repayments of) short-term borrowings	131.6	(81.0)
Investment contract deposits	5,270.2	4,798.7
Investment contract withdrawals	(7,055.6)	(6,126.0)
Net increase (decrease) in banking operation deposits	(276.2)	14.9
Other	(6.3)	(5.8)
Net cash provided by (used in) financing activities	(2,435.2)	(1,209.4)
Net increase (decrease) in cash and cash equivalents	(2,470.1)	(554.9)
Cash and cash equivalents at beginning of period	4,177.2	2,833.9
Cash and cash equivalents at end of period	1,707.1	2,279.0
Principal Financial Group, Inc. Parent Only
Operating activities
Net cash provided by (used in) operating activities	(12.8)	49.2
Investing activities
Dividends and returns of capital received from (contributions to) unconsolidated entities	169.3	539.8
Net change in other investments	(3.2)	(0.2)
Net cash provided by (used in) investing activities	166.1	539.6
Financing activities
Issuance of common stock	80.2	24.7
Acquisition of treasury stock	(153.4)	(272.7)
Dividends to common stockholders	(211.7)	(169.6)
Dividends to preferred stockholders	(24.7)	(16.5)
Issuance of long-term debt		593.8
Net cash provided by (used in) financing activities	(309.6)	159.7
Net increase (decrease) in cash and cash equivalents	(156.3)	748.5
Cash and cash equivalents at beginning of period	207.1	226.7
Cash and cash equivalents at end of period	50.8	975.2
Principal Financial Services, Inc. Only
Operating activities
Net cash provided by (used in) operating activities	870.9	(164.6)
Investing activities
Dividends and returns of capital received from (contributions to) unconsolidated entities	(809.2)	538.6
Net change in other investments	(13.9)	(27.1)
Net cash provided by (used in) investing activities	(823.1)	511.5
Financing activities
Net proceeds from (repayments of) short-term borrowings		(50.0)
Capital received from (dividends and capital paid to) parent	(169.3)	(539.8)
Net cash provided by (used in) financing activities	(169.3)	(589.8)
Net increase (decrease) in cash and cash equivalents	(121.5)	(242.9)
Cash and cash equivalents at beginning of period	612.5	702.4
Cash and cash equivalents at end of period	491.0	459.5
Principal Life Insurance Company and Other Subsidiaries Combined
Operating activities
Net cash provided by (used in) operating activities	1,473.4	2,303.2
Investing activities
Available-for-sale securities: Purchases	(7,012.3)	(6,467.5)
Available-for-sale securities: Sales	1,626.7	946.5
Available-for-sale securities: Maturities	5,783.2	4,702.7
Mortgage loans acquired or originated	(2,020.0)	(1,811.8)
Mortgage loans sold or repaid	1,570.8	1,166.7
Real estate acquired	(59.0)	(114.8)
Net (purchases) sales of property and equipment	(22.7)	(35.6)
Purchases of interest in subsidiaries, net of cash acquired	(1,268.3)	(62.5)
Net change in other investments	(14.1)	(15.6)
Net cash provided by (used in) investing activities	(1,415.7)	(1,691.9)
Financing activities
Proceeds from financing element derivatives	46.7	51.6
Payments for financing element derivatives	(36.9)	(38.3)
Excess tax benefits from share-based payment arrangements	8.6	9.8
Purchase of subsidiary shares from noncontrolling interest	(51.7)
Sale of subsidiary shares to noncontrolling interest	32.1
Issuance of long-term debt	1,108.4	9.1
Principal repayments of long-term debt	(212.2)	(2.1)
Net proceeds from (repayments of) short-term borrowings	(2,113.2)	(13.6)
Capital received from (dividends and capital paid to) parent	809.2	(538.6)
Investment contract deposits	5,270.2	4,798.7
Investment contract withdrawals	(7,055.6)	(6,126.0)
Net increase (decrease) in banking operation deposits	(276.2)	14.9
Other	(6.3)	(5.8)
Net cash provided by (used in) financing activities	(2,476.9)	(1,840.3)
Net increase (decrease) in cash and cash equivalents	(2,419.2)	(1,229.0)
Cash and cash equivalents at beginning of period	4,241.3	2,787.9
Cash and cash equivalents at end of period	1,822.1	1,558.9
Eliminations, Shelf Registration Debt Guarantor
Operating activities
Net cash provided by (used in) operating activities	(933.6)	185.9
Investing activities
Dividends and returns of capital received from (contributions to) unconsolidated entities	639.9	(1,078.4)
Net cash provided by (used in) investing activities	639.9	(1,078.4)
Financing activities
Issuance of long-term debt	(1,084.3)
Net proceeds from (repayments of) short-term borrowings	2,244.8	(17.4)
Capital received from (dividends and capital paid to) parent	(639.9)	1,078.4
Net cash provided by (used in) financing activities	520.6	1,061.0
Net increase (decrease) in cash and cash equivalents	226.9	168.5
Cash and cash equivalents at beginning of period	(883.7)	(883.1)
Cash and cash equivalents at end of period	$ (656.8)	$ (714.6)