Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Sep. 30, 2023 USD ($) item	Dec. 31, 2022 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 13,826.5	$ 45,651.0
Fixed maturities, Less than twelve months, Gross unrealized losses	818.9	6,183.1
Fixed maturities, Greater than or equal to twelve months, Fair value	40,232.1	8,850.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	8,415.0	1,695.2
Fixed maturities, Total, Fair value	54,058.6	54,501.9
Fixed maturities, Total, Gross unrealized losses	9,233.9	7,878.3
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	391.1	1,528.3
Fixed maturities, Less than twelve months, Gross unrealized losses	11.5	209.4
Fixed maturities, Greater than or equal to twelve months, Fair value	1,052.8	181.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	302.0	41.8
Fixed maturities, Total, Fair value	1,443.9	1,709.8
Fixed maturities, Total, Gross unrealized losses	313.5	251.2
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	55.2	407.5
Fixed maturities, Less than twelve months, Gross unrealized losses	6.6	57.7
Fixed maturities, Greater than or equal to twelve months, Fair value	307.9	19.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	80.8	7.1
Fixed maturities, Total, Fair value	363.1	427.4
Fixed maturities, Total, Gross unrealized losses	87.4	64.8
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,258.4	5,303.5
Fixed maturities, Less than twelve months, Gross unrealized losses	106.6	1,008.9
Fixed maturities, Greater than or equal to twelve months, Fair value	4,756.6	391.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,348.9	127.8
Fixed maturities, Total, Fair value	6,015.0	5,695.4
Fixed maturities, Total, Gross unrealized losses	1,455.5	1,136.7
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	7,731.5	27,309.5
Fixed maturities, Less than twelve months, Gross unrealized losses	548.3	3,944.6
Fixed maturities, Greater than or equal to twelve months, Fair value	21,781.1	2,944.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4,872.0	698.0
Fixed maturities, Total, Fair value	29,512.6	30,253.6
Fixed maturities, Total, Gross unrealized losses	5,420.3	4,642.6
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,427.7	1,201.7
Fixed maturities, Less than twelve months, Gross unrealized losses	63.7	97.5
Fixed maturities, Greater than or equal to twelve months, Fair value	1,236.4	574.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	231.4	105.7
Fixed maturities, Total, Fair value	2,664.1	1,776.5
Fixed maturities, Total, Gross unrealized losses	295.1	203.2
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	438.7	3,648.5
Fixed maturities, Less than twelve months, Gross unrealized losses	13.9	484.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,156.5	1,124.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	762.7	222.5
Fixed maturities, Total, Fair value	4,595.2	4,773.3
Fixed maturities, Total, Gross unrealized losses	776.6	706.5
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	258.4	2,832.2
Fixed maturities, Less than twelve months, Gross unrealized losses	2.6	89.0
Fixed maturities, Greater than or equal to twelve months, Fair value	2,530.2	1,330.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	41.5	54.7
Fixed maturities, Total, Fair value	2,788.6	4,162.3
Fixed maturities, Total, Gross unrealized losses	44.1	143.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,265.5	3,419.8
Fixed maturities, Less than twelve months, Gross unrealized losses	65.7	292.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,410.6	2,283.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	775.7	437.6
Fixed maturities, Total, Fair value	6,676.1	5,703.6
Fixed maturities, Total, Gross unrealized losses	841.4	729.6
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	12,608.0	44,857.0
Fixed maturities, Less than twelve months, Gross unrealized losses	737.2	6,096.3
Fixed maturities, Greater than or equal to twelve months, Fair value	39,508.4	8,496.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	8,251.3	1,645.1
Fixed maturities, Total, Fair value	52,116.4	53,353.1
Fixed maturities, Total, Gross unrealized losses	$ 8,988.5	$ 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)	95.00%	94.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	85.00%	87.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months \| item	2,321	7,589
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	94.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	90.00%	95.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 712.2	$ 5,920.4
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	7,223	1,654
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	83.00%	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	$ 1,337.1	$ 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)	78.00%	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	$ 4,735.6	$ 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)	82.00%	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	$ 757.4	$ 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)	84.00%	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	$ 612.3	$ 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)	80.00%	81.00%

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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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