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Basis of presentation - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items] |  |  |
Other assets | $ 3,301 |  | $ 2,443
Other liabilities | $ 4,987 |  | 4,505
cumulative effect adjustment on other assets and other liabilities |  | $ 642 |
CNA Financial [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Subsidiary ownership percentage | 89.00% |  |
Diamond Offshore Drilling, Inc. [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Subsidiary ownership percentage | 53.00% |  |
Consolidated Container [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Subsidiary ownership percentage | 99.00% |  |
Subsequent to Adoption of Accounting Standards Update 2016-02 [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Other assets |  | 3,100 | 2,400
Other liabilities |  | $ 5,100 | $ 4,500

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