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Fair Value Measurements - Proceeds from the Sale of Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Proceeds from the sale of investments in available-for-sale securities, realized gains and losses on those sales, and interest and dividend income
Sale proceeds	$ 13	$ 153
Realized gains	4	7
Realized Losses	(5)	(6)
Interest and dividend income	$ 5	$ 9

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