Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Sep. 30, 2022 USD ($) item	Dec. 31, 2021 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 49,918.0	$ 14,561.3
Fixed maturities, Less than twelve months, Gross unrealized losses	7,525.0	227.1
Fixed maturities, Greater than or equal to twelve months, Fair value	6,895.3	3,042.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,334.6	179.3
Fixed maturities, Total, Fair value	56,813.3	17,603.9
Fixed maturities, Total, Gross unrealized losses	8,859.6	406.4
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,922.3	129.3
Fixed maturities, Less than twelve months, Gross unrealized losses	215.0	3.4
Fixed maturities, Greater than or equal to twelve months, Fair value	123.1	482.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	39.6	34.0
Fixed maturities, Total, Fair value	2,045.4	612.2
Fixed maturities, Total, Gross unrealized losses	254.6	37.4
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	413.6	57.8
Fixed maturities, Less than twelve months, Gross unrealized losses	79.7	2.0
Fixed maturities, Greater than or equal to twelve months, Fair value	11.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	4.5
Fixed maturities, Total, Fair value	424.6	57.8
Fixed maturities, Total, Gross unrealized losses	84.2	2.0
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	5,740.2	690.2
Fixed maturities, Less than twelve months, Gross unrealized losses	1,126.9	10.5
Fixed maturities, Greater than or equal to twelve months, Fair value	257.3	102.3
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	67.4	6.1
Fixed maturities, Total, Fair value	5,997.5	792.5
Fixed maturities, Total, Gross unrealized losses	1,194.3	16.6
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	29,578.7	5,281.6
Fixed maturities, Less than twelve months, Gross unrealized losses	4,984.1	121.2
Fixed maturities, Greater than or equal to twelve months, Fair value	2,443.8	1,327.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	617.4	101.5
Fixed maturities, Total, Fair value	32,022.5	6,609.1
Fixed maturities, Total, Gross unrealized losses	5,601.5	222.7
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,253.5	1,562.6
Fixed maturities, Less than twelve months, Gross unrealized losses	139.1	22.2
Fixed maturities, Greater than or equal to twelve months, Fair value	434.0	194.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	84.0	6.3
Fixed maturities, Total, Fair value	1,687.5	1,757.5
Fixed maturities, Total, Gross unrealized losses	223.1	28.5
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	4,132.0	1,297.4
Fixed maturities, Less than twelve months, Gross unrealized losses	509.6	15.6
Fixed maturities, Greater than or equal to twelve months, Fair value	779.9	299.6
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	144.9	15.7
Fixed maturities, Total, Fair value	4,911.9	1,597.0
Fixed maturities, Total, Gross unrealized losses	654.5	31.3
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,791.0	1,592.5
Fixed maturities, Less than twelve months, Gross unrealized losses	98.0	2.8
Fixed maturities, Greater than or equal to twelve months, Fair value	981.3	424.4
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	38.1	6.7
Fixed maturities, Total, Fair value	3,772.3	2,016.9
Fixed maturities, Total, Gross unrealized losses	136.1	9.5
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	4,086.7	3,949.9
Fixed maturities, Less than twelve months, Gross unrealized losses	372.6	49.4
Fixed maturities, Greater than or equal to twelve months, Fair value	1,864.9	211.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	338.7	9.0
Fixed maturities, Total, Fair value	5,951.6	4,160.9
Fixed maturities, Total, Gross unrealized losses	711.3	58.4
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	48,764.6	13,052.3
Fixed maturities, Less than twelve months, Gross unrealized losses	7,422.5	150.9
Fixed maturities, Greater than or equal to twelve months, Fair value	6,399.5	2,740.3
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,264.1	137.1
Fixed maturities, Total, Fair value	55,164.1	15,792.6
Fixed maturities, Total, Gross unrealized losses	$ 8,686.6	$ 288.0
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%	91.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	86.00%	98.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months | item	8,037	1,805
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	87.00%	99.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	95.00%	90.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 7,171.8	$ 138.9
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer | item	1,304	459
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	84.00%	95.00%
Principal Life Insurance Company | U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses		$ 30.9
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)		93.00%
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	$ 553.7	$ 67.1
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%	95.00%
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	$ 143.5	$ 15.3
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%	95.00%
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	$ 228.1
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%
Principal Life Insurance Company | Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses		$ 6.7
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)		98.00%
Principal Life Insurance Company | Asset backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 107.3
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%