Senior Long-Term Debt and Other Debt Senior Long-Term Debt and Other Debt (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Debt Instrument, Fair Value Disclosure	$ 3,845,000,000	$ 3,845,000,000		$ 3,030,000,000
Line of Credit Facility, Expiration Date	Apr. 10, 2024
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 300,000,000	300,000,000	$ 300,000,000
LineOfCreditFacilityBorrowingCapacityIncrease		200,000,000
Long-term Line of Credit	0	0		$ 0
Secured Letters Of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200,000,000	$ 200,000,000