Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 6,667.6	$ 45,651.0
Fixed maturities, Less than twelve months, Gross unrealized losses	180.0	6,183.1
Fixed maturities, Greater than or equal to twelve months, Fair value	41,511.0	8,850.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,692.9	1,695.2
Fixed maturities, Total, Fair value	48,178.6	54,501.9
Fixed maturities, Total, Gross unrealized losses	5,872.9	7,878.3
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	316.4	1,528.3
Fixed maturities, Less than twelve months, Gross unrealized losses	3.1	209.4
Fixed maturities, Greater than or equal to twelve months, Fair value	997.1	181.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	232.6	41.8
Fixed maturities, Total, Fair value	1,313.5	1,709.8
Fixed maturities, Total, Gross unrealized losses	235.7	251.2
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	41.9	407.5
Fixed maturities, Less than twelve months, Gross unrealized losses	1.7	57.7
Fixed maturities, Greater than or equal to twelve months, Fair value	331.3	19.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	57.9	7.1
Fixed maturities, Total, Fair value	373.2	427.4
Fixed maturities, Total, Gross unrealized losses	59.6	64.8
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	596.6	5,303.5
Fixed maturities, Less than twelve months, Gross unrealized losses	19.0	1,008.9
Fixed maturities, Greater than or equal to twelve months, Fair value	5,075.1	391.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	914.8	127.8
Fixed maturities, Total, Fair value	5,671.7	5,695.4
Fixed maturities, Total, Gross unrealized losses	933.8	1,136.7
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	3,210.1	27,309.5
Fixed maturities, Less than twelve months, Gross unrealized losses	126.9	3,944.6
Fixed maturities, Greater than or equal to twelve months, Fair value	22,929.1	2,944.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	3,064.4	698.0
Fixed maturities, Total, Fair value	26,139.2	30,253.6
Fixed maturities, Total, Gross unrealized losses	3,191.3	4,642.6
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	633.0	1,201.7
Fixed maturities, Less than twelve months, Gross unrealized losses	4.9	97.5
Fixed maturities, Greater than or equal to twelve months, Fair value	1,275.6	574.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	159.7	105.7
Fixed maturities, Total, Fair value	1,908.6	1,776.5
Fixed maturities, Total, Gross unrealized losses	164.6	203.2
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	280.3	3,648.5
Fixed maturities, Less than twelve months, Gross unrealized losses	4.1	484.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,192.4	1,124.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	650.1	222.5
Fixed maturities, Total, Fair value	4,472.7	4,773.3
Fixed maturities, Total, Gross unrealized losses	654.2	706.5
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	405.6	2,832.2
Fixed maturities, Less than twelve months, Gross unrealized losses	1.8	89.0
Fixed maturities, Greater than or equal to twelve months, Fair value	2,301.6	1,330.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	25.4	54.7
Fixed maturities, Total, Fair value	2,707.2	4,162.3
Fixed maturities, Total, Gross unrealized losses	27.2	143.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,183.7	3,419.8
Fixed maturities, Less than twelve months, Gross unrealized losses	18.5	292.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,408.8	2,283.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	588.0	437.6
Fixed maturities, Total, Fair value	5,592.5	5,703.6
Fixed maturities, Total, Gross unrealized losses	606.5	729.6
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	5,836.0	44,857.0
Fixed maturities, Less than twelve months, Gross unrealized losses	140.5	6,096.3
Fixed maturities, Greater than or equal to twelve months, Fair value	40,717.9	8,496.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	5,576.6	1,645.1
Fixed maturities, Total, Fair value	46,553.9	53,353.1
Fixed maturities, Total, Gross unrealized losses	$ 5,717.1	$ 7,741.4
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)	94.00%	94.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	89.00%	87.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months | security	983	7,589
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	98.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	91.00%	95.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 131.2	$ 5,920.4
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer | security	7,042	1,654
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	88.00%	84.00%
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	$ 906.9	$ 126.8
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%	75.00%
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	$ 2,968.9	$ 654.9
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)	88.00%	80.00%
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	$ 645.6	$ 220.9
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)	87.00%	83.00%
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	$ 472.9	$ 320.2
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%	81.00%