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Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions | Sep. 30, 2022 USD ($) item | Dec. 31, 2021 USD ($) item
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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% |

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