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Debt And Liquidity (Narrative) (Details) - USD ($)				1 Months Ended		3 Months Ended		12 Months Ended
	Feb. 17, 2021	Dec. 22, 2020	Feb. 12, 2018	Feb. 28, 2021	Dec. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Jun. 15, 2018	Jun. 14, 2018	Apr. 19, 2018
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage		100.00%
Equity Interest Pledge			65.00%
Repayments of Secured Debt						$ 150,000,000	$ 0
Subordinated Borrowing, Interest Rate		4.625%
Percentage of Principal Amount Redeemed						30.00%
Interest rate swap contract
Debt Instrument [Line Items]
Derivative, Notional Amount							$ 500,000,000
Interest rate swap contract | Not Designated as Hedging Instrument
Debt Instrument [Line Items]
Derivative, Notional Amount					$ 250,000,000			$ 250,000,000
Secured Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 500,000,000
2018 Term Loan Facility
Debt Instrument [Line Items]
Repayments of Secured Debt								900,000,000	$ 350,000,000
2018 Term Loan Facility | Senior Subordinated Notes
Debt Instrument [Line Items]
Repayments of Secured Debt	$ 150,000,000			$ 150,000,000	500,000,000
2018 Credit Agreement
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital			4.00
Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,500,000,000
Debt Instrument, Basis Spread on Variable Rate						0.25%
Debt Instrument, Amortization Rate			5.00%
Excess Cashflow Threshold Percentage			75.00%
Debt Instrument, Interest Rate, Increase (Decrease)	1.00%
Debt Instrument Prepayment Premium			1.00%
Revolving Credit Facility | 2018 Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 250,000,000							$ 2,250,000,000	$ 1,500,000,000
Debt Instrument, Basis Spread on Variable Rate						0.25%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage						0.25%
Borrowing Threshold			$ 35,000,000
Borrowing Threshold Percentage			35.00%
Line of credit upfront fee percentage										1.00%
ABR | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			2.50%
ABR | Revolving Credit Facility | 2018 Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			2.75%
London Interbank Offered Rate (LIBOR) | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.50%
Debt Instrument, Basis Spread on Variable Rate, Increase (Decrease)	0.50%
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | 2018 Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.75%
Contingent Event One | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage			50.00%
Contingent Event Two | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage			0.00%
Minimum | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Increase (Decrease)	0.50%
Minimum | Contingent Event One | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital			1.25
Maximum | Contingent Event One | Line of Credit | 2018 Term Loan Facility
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital			1.75
Brookfield | Brookfield Promissory Note
Debt Instrument [Line Items]
Dividends Payable												$ 750,000,000
Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Long-term Debt, Fair Value					$ 1,453,000,000	$ 1,296,000,000		$ 1,453,000,000

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Debt Instrument, Amortization Rate

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Debt Instrument Prepayment Premium

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Line of credit upfront fee percentage

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Incremental percentage increase (decrease) in the stated rate on a debt instrument.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Percentage of principal amount of debt redeemed.

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Nominal or face amount used to calculate payment on derivative.

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Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Indebtedness divided by net capital.

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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Stated interest rate of the subordinated debt.

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