Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from domestic operations		$ 2,644,000,000	$ 1,753,000,000	$ 704,000,000
Losses from foreign operations		(84,000,000)	0	19,000,000
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Amount		0	(39,000,000)	877,000,000
Deferred Tax Assets, Operating Loss Carryforwards		84,000,000	521,000,000
Current State and Local Tax Expense (Benefit)		5,000,000	4,000,000	5,000,000
Deferred Tax Assets, Valuation Allowance		4,000,000	0
Tax Cuts and Jobs Act, Income Tax Expense (Benefit)				877,000,000
Tax Cuts and Jobs Act, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense				821,000,000
Tax Cuts and Jobs Act of 2017, Deferred Tax Asset, Income Tax Expense (Benefit), Sequestration Fee Payable			56,000,000	56,000,000
Tax Cuts and Jobs Act, Measurement Period Adjustment, Income Tax Expense (Benefit)			17,000,000
Tax Cuts and Jobs Act, Accounting Complete, Date			39,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		410,000,000
Income Tax Credits and Adjustments		11,000,000
Income Tax Examination, Penalties and Interest Expense		1,000,000	0	$ 0
Income Tax Examination, Interest Accrued		0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		0
Income Tax Examination, Penalties Accrued		0
Alternative Minimum Tax (AMT) credits [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Income Tax Refunds	$ 421,000,000
UNITED STATES
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		77,000,000
UNITED KINGDOM
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		3,000,000
Foreign Tax Authority [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		4,000,000
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards			$ 477,000,000
Income Taxes Receivable, Current		$ 5,000,000