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Quarterly Operating Results (Unaudited) - Realized gains (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018
Realized gains (losses) |  |  |  |  |  |  |  |  |  |
Realized Gains (Losses) on Securities and Subsidiaries | $ (2) | $ (3) | $ 12 | $ 2 | $ (15) | $ 1 | $ 8 | $ 2 | $ 9 | $ (4)
Equity securities | Accounting Standards Update 2016-01 |  |  |  |  |  |  |  |  |  |
Realized gains (losses) |  |  |  |  |  |  |  |  |  |
Realized Gains (Losses) on Securities and Subsidiaries | $ 67 | $ (15) | $ 44 | $ 182 | $ (223) | $ 33 | $ 23 | $ (95) | $ 278 | $ (262)

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