Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Senior Notes [Member] | |||
Debt Instrument [Line Items] | |||
Extinguishment of debt | $ 933 | $ 793 | |
Senior Notes [Member] | Change Of Control And Loss Of Investment Grade Rating [Member] | |||
Debt Instrument [Line Items] | |||
Required purchase price as percentage of aggregate principal amount | 101.00% | ||
Reported Value Measurement [Member] | |||
Debt Instrument [Line Items] | |||
Fair value of long term debt | $ 13,900 | 13,900 | |
Level 2 [Member] | Estimate of Fair Value Measurement [Member] | |||
Debt Instrument [Line Items] | |||
Fair value of long term debt | $ 15,300 | $ 15,100 |