Fair Value Measurements And Disclosure (Fair Value Leveling) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Debt Securities (at fair value)	$ 881	$ 581
Domestic Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	1,279	1,142
International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	291	321
Fixed Income Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	149	152
Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)		17
Liability Derivatives (at fair value)	(90)	(31)
Cross-Currency Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	1,330	1,753
Liability Derivatives (at fair value)	(1,614)	(1,290)
Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	52
Liability Derivatives (at fair value)	(3)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Debt Securities (at fair value)	0	0
Level 1 [Member] | Domestic Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	1,279	1,142
Level 1 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	291	321
Level 1 [Member] | Fixed Income Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	149	0
Level 1 [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)		0
Liability Derivatives (at fair value)	0	0
Level 1 [Member] | Cross-Currency Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	0	0
Liability Derivatives (at fair value)	0	0
Level 1 [Member] | Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	0
Liability Derivatives (at fair value)	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Debt Securities (at fair value)	881	581
Level 2 [Member] | Domestic Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	0
Level 2 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	0
Level 2 [Member] | Fixed Income Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	152
Level 2 [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)		17
Liability Derivatives (at fair value)	(90)	(31)
Level 2 [Member] | Cross-Currency Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	1,330	1,753
Liability Derivatives (at fair value)	(1,614)	(1,290)
Level 2 [Member] | Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	52
Liability Derivatives (at fair value)	(3)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Debt Securities (at fair value)	0	0
Level 3 [Member] | Domestic Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	0
Level 3 [Member] | International Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	0
Level 3 [Member] | Fixed Income Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities (at fair value)	0	0
Level 3 [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)		0
Liability Derivatives (at fair value)	0	0
Level 3 [Member] | Cross-Currency Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	0	0
Liability Derivatives (at fair value)	0	$ 0
Level 3 [Member] | Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Derivatives (at fair value)	0
Liability Derivatives (at fair value)	$ 0