Fair Value - Quantitative Information about Significant Unobservable Inputs Utilized by Company in Fair Value Measurements of Level 3 Assets (Detail) $ in Millions	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value	$ 42,187	$ 39,542
Level 3 [Member] | Fixed Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value	$ 525	$ 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	0.06	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	0.02	0.03