Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Jun. 30, 2026 USD ($) item	Dec. 31, 2025 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 13,295.9	$ 6,056.3
Fixed maturities, Less than twelve months, Gross unrealized losses	196.5	125.7
Fixed maturities, Greater than or equal to twelve months, Fair value	31,012.7	33,571.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,220.1	5,096.3
Fixed maturities, Total, Fair value	44,308.6	39,627.3
Fixed maturities, Total, Gross unrealized losses	5,416.6	5,222.0
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	792.8	484.1
Fixed maturities, Less than twelve months, Gross unrealized losses	17.4	11.0
Fixed maturities, Greater than or equal to twelve months, Fair value	818.8	734.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	273.9	257.1
Fixed maturities, Total, Fair value	1,611.6	1,218.2
Fixed maturities, Total, Gross unrealized losses	291.3	268.1
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	28.2	12.8
Fixed maturities, Less than twelve months, Gross unrealized losses	0.8	0.3
Fixed maturities, Greater than or equal to twelve months, Fair value	198.8	310.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	38.7	54.3
Fixed maturities, Total, Fair value	227.0	323.7
Fixed maturities, Total, Gross unrealized losses	39.5	54.6
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	392.6	639.4
Fixed maturities, Less than twelve months, Gross unrealized losses	6.6	8.9
Fixed maturities, Greater than or equal to twelve months, Fair value	4,700.0	4,903.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,014.2	1,003.0
Fixed maturities, Total, Fair value	5,092.6	5,542.9
Fixed maturities, Total, Gross unrealized losses	1,020.8	1,011.9
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	4,180.1	1,889.9
Fixed maturities, Less than twelve months, Gross unrealized losses	110.2	95.7
Fixed maturities, Greater than or equal to twelve months, Fair value	18,002.6	19,474.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	3,068.7	2,970.8
Fixed maturities, Total, Fair value	22,182.7	21,364.5
Fixed maturities, Total, Gross unrealized losses	3,178.9	3,066.5
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,001.7	201.2
Fixed maturities, Less than twelve months, Gross unrealized losses	10.9	0.7
Fixed maturities, Greater than or equal to twelve months, Fair value	967.1	1,147.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	123.8	117.3
Fixed maturities, Total, Fair value	1,968.8	1,348.8
Fixed maturities, Total, Gross unrealized losses	134.7	118.0
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,433.2	342.0
Fixed maturities, Less than twelve months, Gross unrealized losses	16.8	2.5
Fixed maturities, Greater than or equal to twelve months, Fair value	3,150.8	3,465.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	302.7	301.6
Fixed maturities, Total, Fair value	4,584.0	3,807.9
Fixed maturities, Total, Gross unrealized losses	319.5	304.1
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,112.0	1,919.9
Fixed maturities, Less than twelve months, Gross unrealized losses	10.2	4.7
Fixed maturities, Greater than or equal to twelve months, Fair value	73.2	20.2
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5.3	5.0
Fixed maturities, Total, Fair value	2,185.2	1,940.1
Fixed maturities, Total, Gross unrealized losses	15.5	9.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	3,355.3	567.0
Fixed maturities, Less than twelve months, Gross unrealized losses	23.6	1.9
Fixed maturities, Greater than or equal to twelve months, Fair value	3,101.4	3,514.2
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	392.8	387.2
Fixed maturities, Total, Fair value	6,456.7	4,081.2
Fixed maturities, Total, Gross unrealized losses	416.4	389.1
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	12,851.2	5,888.1
Fixed maturities, Less than twelve months, Gross unrealized losses	183.4	117.8
Fixed maturities, Greater than or equal to twelve months, Fair value	30,427.4	32,859.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,144.0	5,032.1
Fixed maturities, Total, Fair value	43,278.6	38,748.0
Fixed maturities, Total, Gross unrealized losses	$ 5,327.4	$ 5,149.9
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)	89.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months \| item	1,903	870
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	99.00%	98.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	94.00%	93.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 154.6	$ 96.7
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	5,460	5,758
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	87.00%
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	$ 1,007.1	$ 996.0
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)	82.00%	83.00%
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	$ 3,005.2	$ 2,919.0
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)	85.00%	87.00%
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	$ 302.0	$ 301.0
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)	91.00%	92.00%
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	$ 367.7	$ 356.7
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%	87.00%

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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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