Income Taxes (Narrative) (One-time Transaction) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2020 INR (₨)	Dec. 31, 2019 USD ($)	Apr. 30, 2018 INR (₨)
One-time Transaction [Table] [Line Items]
Income tax expense	$ 142	$ 142
Restricted investments						$ 414
Short-term Investments [Member]
One-time Transaction [Table] [Line Items]
Restricted investments						414
Long-term investments [Member]
One-time Transaction [Table] [Line Items]
Restricted investments	393
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member]
One-time Transaction [Table] [Line Items]
Deposits assets	$ 66				₨ 5,000,000,000	70
Desposits assets, percent disputed tax amount	15.00%				15.00%
Restricted investments initially deposited	$ 372					393	₨ 28,000,000,000
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | Other Current Assets [Member]
One-time Transaction [Table] [Line Items]
Deposits assets						$ 70
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | Other Noncurrent Assets [Member]
One-time Transaction [Table] [Line Items]
Deposits assets	66
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | 2016 India Cash Remittance [Member]
One-time Transaction [Table] [Line Items]
Foreign earnings repatriated			$ 2,800
Income tax expense			$ 135
Income tax, disputed amount	$ 438				₨ 33,000,000,000
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | 2013 India Share Repurchase [Member]
One-time Transaction [Table] [Line Items]
Foreign earnings repatriated				$ 523