Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Mar. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 27,258.4	$ 45,651.0
Fixed maturities, Less than twelve months, Gross unrealized losses	2,296.0	6,183.1
Fixed maturities, Greater than or equal to twelve months, Fair value	26,097.6	8,850.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4,343.9	1,695.2
Fixed maturities, Total, Fair value	53,356.0	54,501.9
Fixed maturities, Total, Gross unrealized losses	6,639.9	7,878.3
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	879.6	1,528.3
Fixed maturities, Less than twelve months, Gross unrealized losses	86.0	209.4
Fixed maturities, Greater than or equal to twelve months, Fair value	605.2	181.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	127.3	41.8
Fixed maturities, Total, Fair value	1,484.8	1,709.8
Fixed maturities, Total, Gross unrealized losses	213.3	251.2
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	257.4	407.5
Fixed maturities, Less than twelve months, Gross unrealized losses	21.4	57.7
Fixed maturities, Greater than or equal to twelve months, Fair value	131.5	19.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	34.5	7.1
Fixed maturities, Total, Fair value	388.9	427.4
Fixed maturities, Total, Gross unrealized losses	55.9	64.8
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	3,191.6	5,303.5
Fixed maturities, Less than twelve months, Gross unrealized losses	372.3	1,008.9
Fixed maturities, Greater than or equal to twelve months, Fair value	2,251.2	391.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	537.3	127.8
Fixed maturities, Total, Fair value	5,442.8	5,695.4
Fixed maturities, Total, Gross unrealized losses	909.6	1,136.7
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	17,165.8	27,309.5
Fixed maturities, Less than twelve months, Gross unrealized losses	1,571.1	3,944.6
Fixed maturities, Greater than or equal to twelve months, Fair value	12,333.1	2,944.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	2,303.7	698.0
Fixed maturities, Total, Fair value	29,498.9	30,253.6
Fixed maturities, Total, Gross unrealized losses	3,874.8	4,642.6
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	616.0	1,201.7
Fixed maturities, Less than twelve months, Gross unrealized losses	16.4	97.5
Fixed maturities, Greater than or equal to twelve months, Fair value	1,159.9	574.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	156.5	105.7
Fixed maturities, Total, Fair value	1,775.9	1,776.5
Fixed maturities, Total, Gross unrealized losses	172.9	203.2
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	996.4	3,648.5
Fixed maturities, Less than twelve months, Gross unrealized losses	78.4	484.0
Fixed maturities, Greater than or equal to twelve months, Fair value	3,749.0	1,124.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	548.6	222.5
Fixed maturities, Total, Fair value	4,745.4	4,773.3
Fixed maturities, Total, Gross unrealized losses	627.0	706.5
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,738.4	2,832.2
Fixed maturities, Less than twelve months, Gross unrealized losses	33.5	89.0
Fixed maturities, Greater than or equal to twelve months, Fair value	2,484.8	1,330.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	97.5	54.7
Fixed maturities, Total, Fair value	4,223.2	4,162.3
Fixed maturities, Total, Gross unrealized losses	131.0	143.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,413.2	3,419.8
Fixed maturities, Less than twelve months, Gross unrealized losses	116.9	292.0
Fixed maturities, Greater than or equal to twelve months, Fair value	3,382.9	2,283.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	538.5	437.6
Fixed maturities, Total, Fair value	5,796.1	5,703.6
Fixed maturities, Total, Gross unrealized losses	655.4	729.6
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	26,573.1	44,857.0
Fixed maturities, Less than twelve months, Gross unrealized losses	2,243.3	6,096.3
Fixed maturities, Greater than or equal to twelve months, Fair value	25,409.5	8,496.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4,250.5	1,645.1
Fixed maturities, Total, Fair value	51,982.6	53,353.1
Fixed maturities, Total, Gross unrealized losses	$ 6,493.8	$ 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 \| item	4,895	7,589
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	92.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	94.00%	95.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 2,170.6	$ 5,920.4
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	5,130	1,654
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	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	$ 530.8	$ 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)	81.00%	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	$ 2,228.7	$ 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)	84.00%	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	$ 544.5	$ 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	$ 415.0	$ 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)	84.00%	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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Amount of accumulated unrealized loss on 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 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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