Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	Nov. 01, 2020	Aug. 01, 2020	Sep. 30, 2020	Jun. 12, 2020	Dec. 31, 2019	Dec. 31, 2010	Jul. 31, 2010
Debt Instrument [Line Items]
Principal Amount			$ 3,736		$ 3,500
Unamortized Debt Issuance Cost			29		30
Senior Notes [Member] | 3.375% Senior Notes Due 2030 [Member]
Debt Instrument [Line Items]
Principal Amount			300	$ 300	0
Senior Notes [Member] | 6 1/2% GO Zone Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Principal Amount			0		100		$ 100
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed		100.00%
Extinguishment of Debt, Amount		$ 100
Senior Notes [Member] | 2035 GO Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Principal Amount			89		89	$ 89
Senior Notes [Member] | 2035 IKE Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Principal Amount			$ 65		$ 65	$ 65
Subsequent Event [Member] | Senior Notes [Member] | 2035 GO Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%
Extinguishment of Debt, Amount	$ 89
Subsequent Event [Member] | Senior Notes [Member] | 2035 IKE Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%
Extinguishment of Debt, Amount	$ 65