Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Jun. 30, 2025 USD ($) item	Dec. 31, 2024 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 9,386.2	$ 11,600.7
Fixed maturities, Less than twelve months, Gross unrealized losses	263.1	273.4
Fixed maturities, Greater than or equal to twelve months, Fair value	33,376.0	34,766.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,574.1	6,201.8
Fixed maturities, Total, Fair value	42,762.2	46,367.3
Fixed maturities, Total, Gross unrealized losses	5,837.2	6,475.2
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	459.6	909.1
Fixed maturities, Less than twelve months, Gross unrealized losses	12.9	17.4
Fixed maturities, Greater than or equal to twelve months, Fair value	637.0	810.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	256.2	283.1
Fixed maturities, Total, Fair value	1,096.6	1,719.7
Fixed maturities, Total, Gross unrealized losses	269.1	300.5
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	27.2	32.9
Fixed maturities, Less than twelve months, Gross unrealized losses	0.7	1.3
Fixed maturities, Greater than or equal to twelve months, Fair value	298.3	308.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	73.0	83.2
Fixed maturities, Total, Fair value	325.5	341.7
Fixed maturities, Total, Gross unrealized losses	73.7	84.5
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	904.2	743.2
Fixed maturities, Less than twelve months, Gross unrealized losses	32.0	26.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,675.8	4,745.7
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,086.7	1,115.8
Fixed maturities, Total, Fair value	5,580.0	5,488.9
Fixed maturities, Total, Gross unrealized losses	1,118.7	1,141.8
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	3,934.0	4,970.7
Fixed maturities, Less than twelve months, Gross unrealized losses	187.9	164.2
Fixed maturities, Greater than or equal to twelve months, Fair value	19,269.5	20,099.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	3,206.3	3,532.3
Fixed maturities, Total, Fair value	23,203.5	25,069.8
Fixed maturities, Total, Gross unrealized losses	3,394.2	3,696.5
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	799.3	1,938.4
Fixed maturities, Less than twelve months, Gross unrealized losses	8.3	33.2
Fixed maturities, Greater than or equal to twelve months, Fair value	1,177.2	1,214.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	146.6	182.6
Fixed maturities, Total, Fair value	1,976.5	3,152.4
Fixed maturities, Total, Gross unrealized losses	154.9	215.8
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	388.0	691.7
Fixed maturities, Less than twelve months, Gross unrealized losses	3.4	8.2
Fixed maturities, Greater than or equal to twelve months, Fair value	3,734.2	3,860.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	346.1	442.6
Fixed maturities, Total, Fair value	4,122.2	4,551.8
Fixed maturities, Total, Gross unrealized losses	349.5	450.8
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,630.5	582.2
Fixed maturities, Less than twelve months, Gross unrealized losses	6.6	1.3
Fixed maturities, Greater than or equal to twelve months, Fair value	12.1	29.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4.3	5.0
Fixed maturities, Total, Fair value	1,642.6	612.0
Fixed maturities, Total, Gross unrealized losses	10.9	6.3
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,243.4	1,732.5
Fixed maturities, Less than twelve months, Gross unrealized losses	11.3	21.8
Fixed maturities, Greater than or equal to twelve months, Fair value	3,571.9	3,698.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	454.9	557.2
Fixed maturities, Total, Fair value	4,815.3	5,431.0
Fixed maturities, Total, Gross unrealized losses	466.2	579.0
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	8,832.4	10,805.4
Fixed maturities, Less than twelve months, Gross unrealized losses	225.4	252.3
Fixed maturities, Greater than or equal to twelve months, Fair value	32,802.5	34,145.3
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,498.5	6,121.5
Fixed maturities, Total, Fair value	41,634.9	44,950.7
Fixed maturities, Total, Gross unrealized losses	$ 5,723.9	$ 6,373.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Percent Investment Grade (as a percent)	97.00%	97.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	88.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months \| item	1,361	1,747
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	97.00%	98.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	96.00%	96.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 223.2	$ 245.4
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	5,949	6,219
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	85.00%
Principal Life Insurance Company \| States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 1,079.2	$ 1,108.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	81.00%	81.00%
Principal Life Insurance Company \| Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 3,146.5	$ 3,470.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	85.00%
Principal Life Insurance Company \| Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 345.2	$ 441.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	92.00%	90.00%
Principal Life Insurance Company \| Collateralized mortgage obligation security
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 411.6	$ 490.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	85.00%	83.00%

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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