Long-Term Debt (Schedule Of Long-Term Debt) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
Mar. 31, 2019 | Dec. 31, 2018 |
Debt Instrument [Line Items] | | |
Total long-term debt | $ 6,476 | $ 6,476 |
Unamortized discount and debt issuance costs | (41) | (41) |
Less amount due currently | (600) | (600) |
Long-term debt, less amounts due currently | 5,835 | 5,835 |
Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 6,126 | 6,126 |
2.15% Fixed Senior Notes Due June 1, 2019 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 2.15% | |
2.15% Fixed Senior Notes Due June 1, 2019 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 250 | $ 250 |
5.75% Fixed Senior Notes Due September 30, 2020 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 5.75% | 5.75% |
Due date | Sep. 30, 2020 | Sep. 30, 2020 |
5.75% Fixed Senior Notes Due September 30, 2020 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 126 | $ 126 |
4.10% Fixed Senior Notes Due June 1, 2022 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 4.10% | 4.10% |
4.10% Fixed Senior Notes Due June 1, 2022 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 400 | $ 400 |
7.00% Fixed Debentures Due September 1, 2022 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 7.00% | 7.00% |
7.00% Fixed Debentures Due September 1, 2022 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 482 | $ 482 |
2.95% Fixed Senior Notes Due April 1, 2025 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 2.95% | 2.95% |
2.95% Fixed Senior Notes Due April 1, 2025 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 350 | $ 350 |
3.70% Fixed Senior Notes Due November 15, 2028 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 3.70% | 3.70% |
3.70% Fixed Senior Notes Due November 15, 2028 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 350 | $ 350 |
5.75% Fixed Senior Notes Due March 15, 2029 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 5.75% | 5.75% |
Due date | Mar. 15, 2029 | Mar. 15, 2029 |
5.75% Fixed Senior Notes Due March 15, 2029 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 318 | $ 318 |
7.00% Fixed Senior Notes Due May 1, 2032 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 7.00% | 7.00% |
7.00% Fixed Senior Notes Due May 1, 2032 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 500 | $ 500 |
7.25% Fixed Senior Notes Due January 15, 2033 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 7.25% | 7.25% |
7.25% Fixed Senior Notes Due January 15, 2033 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 350 | $ 350 |
7.50% Fixed Senior Notes Due September 1, 2038 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 7.50% | 7.50% |
7.50% Fixed Senior Notes Due September 1, 2038 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 300 | $ 300 |
5.25% Fixed Senior Notes Due September 30, 2040 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 5.25% | 5.25% |
5.25% Fixed Senior Notes Due September 30, 2040 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 475 | $ 475 |
4.55% Fixed Senior Notes Due December 1, 2041 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 4.55% | 4.55% |
4.55% Fixed Senior Notes Due December 1, 2041 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 400 | $ 400 |
5.30% Fixed Senior Notes Due June 1, 2042 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 5.30% | 5.30% |
5.30% Fixed Senior Notes Due June 1, 2042 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 500 | $ 500 |
3.75% Fixed Senior Notes Due April 1, 2045 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 3.75% | 3.75% |
Due date | Apr. 1, 2045 | Apr. 1, 2045 |
3.75% Fixed Senior Notes Due April 1, 2045 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 550 | $ 550 |
3.80% Fixed Senior Notes Due September 30, 2047 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 3.80% | 3.80% |
Due date | Sep. 30, 2047 | Sep. 30, 2047 |
3.80% Fixed Senior Notes Due September 30, 2047 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 325 | $ 325 |
4.10% Fixed Senior Notes Due November 15, 2048 [Member] | | |
Debt Instrument [Line Items] | | |
Interest percentage | 4.10% | 4.10% |
Due date | Nov. 15, 2048 | Nov. 15, 2048 |
4.10% Fixed Senior Notes Due November 15, 2048 [Member] | Secured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Secured long-term debt | $ 450 | $ 450 |
Term Loan Credit Agreement Maturing December 9, 2019 [Member] | | |
Debt Instrument [Line Items] | | |
Due date | Dec. 9, 2019 | Dec. 9, 2019 |
Term Loan Credit Agreement Maturing December 9, 2019 [Member] | Unsecured Debt [Member] | | |
Debt Instrument [Line Items] | | |
Term loan | $ 350 | $ 350 |