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Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Jan. 01, 2018
OTTI Gains (Losses) [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on change in other comprehensive income (loss) before reclassifications | $ (1) | $ 2 |
Tax on reclassification from accumulated other comprehensive income | 0 | 0 |
Unrealized Gains (Losses) on Investments [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on change in other comprehensive income (loss) before reclassifications | (140) | 105 |
Tax on reclassification from accumulated other comprehensive income | (1) | 4 |
Cash Flow Hedges [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on change in other comprehensive income (loss) before reclassifications | 2 | (2) |
Tax on reclassification from accumulated other comprehensive income | 0 | 0 |
Pension Liability [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on change in other comprehensive income (loss) before reclassifications | 0 | 0 |
Tax on reclassification from accumulated other comprehensive income | (2) | (3) |
Foreign Currency Translation [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on change in other comprehensive income (loss) before reclassifications | 0 | 0 |
Tax on reclassification from accumulated other comprehensive income | $ 0 | $ 0 |
Accounting Standards Update 2016-01 [Member] | OTTI Gains (Losses) [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on cumulative effect adjustment for adoption of ASU 2016-01 |  |  | $ 0
Accounting Standards Update 2016-01 [Member] | Unrealized Gains (Losses) on Investments [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on cumulative effect adjustment for adoption of ASU 2016-01 |  |  | 8
Accounting Standards Update 2016-01 [Member] | Cash Flow Hedges [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on cumulative effect adjustment for adoption of ASU 2016-01 |  |  | 0
Accounting Standards Update 2016-01 [Member] | Pension Liability [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on cumulative effect adjustment for adoption of ASU 2016-01 |  |  | 0
Accounting Standards Update 2016-01 [Member] | Foreign Currency Translation [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax on cumulative effect adjustment for adoption of ASU 2016-01 |  |  | $ 0

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