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Distribution of the Maturity Dates for Fixed Maturity Securities (Detail) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Available-for-Sale Securities, Total Amortized Cost |  |
1 year or less | $ 1,694.9 | $ 1,625.1
Over 1 year through 5 years | 5,665.0 | 5,579.9
Over 5 years through 10 years | 12,273.8 | 12,091.1
Over 10 years | 18,741.8 | 18,611.2
Available-for-sale Securities, Debt Maturities, Gross Subtotal | 38,375.5 | 37,907.3
Mortgage/Asset-Backed Securities | 1,776.4 | 1,873.2
Amortized Cost of Fixed Maturity Securities | 40,151.9 | 39,780.5
Available-for-Sale Securities, Unrealized Gain Position, Gross Gain |  |
1 year or less | 23.4 | 30.9
Over 1 year through 5 years | 372.0 | 453.6
Over 5 years through 10 years | 903.8 | 1,169.8
Over 10 years | 3,261.0 | 4,041.4
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal | 4,560.2 | 5,695.7
Mortgage/Asset-Backed Securities | 81.1 | 105.1
Total Fixed Maturity Securities | 4,641.3 | 5,800.8
Fair Value Maturity Distribution |  |
Fixed Maturity Securities | 44,500.1 |
Available-for-Sale Securities, Unrealized Loss Position, Gross Loss |  |
1 year or less | 4.1 | 3.1
Over 1 year through 5 years | 22.3 | 18.5
Over 5 years through 10 years | 138.1 | 53.2
Over 10 years | 113.9 | 44.0
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Loss, Gross Subtotal | 278.4 | 118.8
Mortgage/Asset-Backed Securities | 14.7 | 4.7
Total Fixed Maturity Securities | 293.1 | 123.5
Fair Value of Fixed Maturity Securities in Unrealized Gain Position |  |
Fair Value Maturity Distribution |  |
1 year or less | 1,645.0 | 1,638.8
Over 1 year through 5 years | 5,680.4 | 5,810.9
Over 5 years through 10 years | 9,124.4 | 11,916.5
Over 10 years | 19,099.4 | 21,333.1
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal | 35,549.2 | 40,699.3
Mortgage/Asset-Backed Securities | 1,362.4 | 1,576.4
Fixed Maturity Securities | 36,911.6 | 42,275.7
Fair Value of Fixed Maturity Securities in Unrealized Loss Position |  |
Fair Value Maturity Distribution |  |
1 year or less | 69.2 | 14.1
Over 1 year through 5 years | 334.3 | 204.1
Over 5 years through 10 years | 3,915.1 | 1,291.2
Over 10 years | 2,789.5 | 1,275.5
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal | 7,108.1 | 2,784.9
Mortgage/Asset-Backed Securities | 480.4 | 397.2
Fixed Maturity Securities | $ 7,588.5 | $ 3,182.1

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