Investments - Gross Unrealized Losses for Fixed Maturities (Details)	Jun. 30, 2022 USD ($) item	Dec. 31, 2021 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 53,580,800,000	$ 14,561,300,000
Fixed maturities, Less than twelve months, Gross unrealized losses	5,282,400,000	227,100,000
Fixed maturities, Greater than or equal to twelve months, Fair value	3,006,900,000	3,042,600,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	473,200,000	179,300,000
Fixed maturities, Total, Fair value	56,587,700,000	17,603,900,000
Fixed maturities, Total, Gross unrealized losses	5,755,600,000	406,400,000
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,018,200,000	129,300,000
Fixed maturities, Less than twelve months, Gross unrealized losses	135,200,000	3,400,000
Fixed maturities, Greater than or equal to twelve months, Fair value	122,600,000	482,900,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	29,900,000	34,000,000.0
Fixed maturities, Total, Fair value	2,140,800,000	612,200,000
Fixed maturities, Total, Gross unrealized losses	165,100,000	37,400,000
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	401,500,000	57,800,000
Fixed maturities, Less than twelve months, Gross unrealized losses	50,300,000	2,000,000.0
Fixed maturities, Greater than or equal to twelve months, Fair value	2,900,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	1,200,000
Fixed maturities, Total, Fair value	404,400,000	57,800,000
Fixed maturities, Total, Gross unrealized losses	51,500,000	2,000,000.0
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	5,715,100,000	690,200,000
Fixed maturities, Less than twelve months, Gross unrealized losses	689,600,000	10,500,000
Fixed maturities, Greater than or equal to twelve months, Fair value	112,000,000.0	102,300,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	25,600,000	6,100,000
Fixed maturities, Total, Fair value	5,827,100,000	792,500,000
Fixed maturities, Total, Gross unrealized losses	715,200,000	16,600,000
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	30,279,200,000	5,281,600,000
Fixed maturities, Less than twelve months, Gross unrealized losses	3,345,400,000	121,200,000
Fixed maturities, Greater than or equal to twelve months, Fair value	1,310,800,000	1,327,500,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	271,700,000	101,500,000
Fixed maturities, Total, Fair value	31,590,000,000.0	6,609,100,000
Fixed maturities, Total, Gross unrealized losses	3,617,100,000	222,700,000
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,636,000,000.0	1,562,600,000
Fixed maturities, Less than twelve months, Gross unrealized losses	123,600,000	22,200,000
Fixed maturities, Greater than or equal to twelve months, Fair value	112,900,000	194,900,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	20,200,000	6,300,000
Fixed maturities, Total, Fair value	1,748,900,000	1,757,500,000
Fixed maturities, Total, Gross unrealized losses	143,800,000	28,500,000
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	4,846,600,000	1,297,400,000
Fixed maturities, Less than twelve months, Gross unrealized losses	413,000,000.0	15,600,000
Fixed maturities, Greater than or equal to twelve months, Fair value	312,100,000	299,600,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	40,300,000	15,700,000
Fixed maturities, Total, Fair value	5,158,700,000	1,597,000,000.0
Fixed maturities, Total, Gross unrealized losses	453,300,000	31,300,000
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	2,940,200,000	1,592,500,000
Fixed maturities, Less than twelve months, Gross unrealized losses	89,900,000	2,800,000
Fixed maturities, Greater than or equal to twelve months, Fair value	651,900,000	424,400,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	21,500,000	6,700,000
Fixed maturities, Total, Fair value	3,592,100,000	2,016,900,000
Fixed maturities, Total, Gross unrealized losses	111,400,000	9,500,000
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	5,744,000,000.0	3,949,900,000
Fixed maturities, Less than twelve months, Gross unrealized losses	435,400,000	49,400,000
Fixed maturities, Greater than or equal to twelve months, Fair value	381,700,000	211,000,000.0
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	62,800,000	9,000,000.0
Fixed maturities, Total, Fair value	6,125,700,000	4,160,900,000
Fixed maturities, Total, Gross unrealized losses	498,200,000	58,400,000
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	52,512,800,000	13,052,300,000
Fixed maturities, Less than twelve months, Gross unrealized losses	5,220,400,000	150,900,000
Fixed maturities, Greater than or equal to twelve months, Fair value	2,598,100,000	2,740,300,000
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	416,900,000	137,100,000
Fixed maturities, Total, Fair value	55,110,900,000	15,792,600,000
Fixed maturities, Total, Gross unrealized losses	$ 5,637,300,000	$ 288,000,000.0
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)	91.00%	98.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months | item	7,710	1,805
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	91.00%	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	$ 4,953,900,000	$ 138,900,000
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer | item	585	459
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	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	$ 29,900,000	$ 30,900,000
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%	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	$ 224,300,000	$ 67,100,000
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%	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	$ 39,400,000	$ 15,300,000
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%	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	$ 39,200,000
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%
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		$ 6,700,000
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%