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Fair Value - Quantitative Information about Significant Unobservable Inputs Utilized by Company in Fair Value Measurements of Level 3 Assets (Detail)
$ in Millions
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated fair value $ 40,525 $ 39,542
Level 3 [Member] | Fixed Maturity Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Estimated fair value $ 293 $ 228
Minimum [Member] | Level 3 [Member] | Credit Spread [Member] | Discounted Cash Flow [Member] | Fixed Maturity Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Measurement input 0.01 0.01
Maximum [Member] | Level 3 [Member] | Credit Spread [Member] | Discounted Cash Flow [Member] | Fixed Maturity Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Measurement input 0.05 0.12
Weighted Average [Member] | Level 3 [Member] | Credit Spread [Member] | Discounted Cash Flow [Member] | Fixed Maturity Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Measurement input 0.03 0.03