Investments - Schedule of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,941	$ 1,692
Gross Unrealized Gains	7	0
Gross Unrealized Losses	2	11
Estimated Fair Value	1,946	1,681
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,174	1,131
Gross Unrealized Gains	5	0
Gross Unrealized Losses	1	8
Estimated Fair Value	1,178	1,123
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	420
Gross Unrealized Gains	1
Gross Unrealized Losses	1
Estimated Fair Value	420
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	126	83
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	1
Estimated Fair Value	127	82
U.S. Treasury notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	86	181
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	86	181
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	78	115
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	1
Estimated Fair Value	78	114
GSEs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49	164
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	1
Estimated Fair Value	49	163
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7	4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	7	4
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1	14
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1	$ 14

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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