Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Assets Measured on a Recurring Basis (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) firm	Mar. 31, 2019 USD ($)	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Number of firms to value preferred stock and bond portfolios | firm	1
Number of firms utilized to value Level 3 other-long term investments | firm	1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	$ (59)	$ (4)
Other Long-Term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	(59)	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	0
Paid-in-kind dividends	0
Purchases	0
Sales and maturities	0
Net valuation (loss) gain included in earnings	0
Corporate Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	0	(4)
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, Beginning of period	138	118
Paid-in-kind dividends	2	2
Purchases	0	5
Sales and maturities	0	(1)
Net valuation (loss) gain included in earnings	(66)	5
Fair value, End of period	15	125
Level 3 | Other Long-Term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, Beginning of period	120	101
Paid-in-kind dividends	2	1
Purchases	0	0
Sales and maturities	0	0
Net valuation (loss) gain included in earnings	(63)	5
Fair value, End of period	0	107
Level 3 | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, Beginning of period	1
Fair value, End of period	1
Level 3 | Corporate Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, Beginning of period	17	17
Paid-in-kind dividends	0	1
Purchases	0	5
Sales and maturities	0	(1)
Net valuation (loss) gain included in earnings	(3)	0
Fair value, End of period	$ 14	$ 18
Level 3 | Measurement Input, Discount Rate | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, discount rate			0.068
Level 3 | Measurement Input, Discount Rate | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, discount rate			0.074
Level 3 | Measurement Input, Discount Rate | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, discount rate			0.070