Income Taxes (Narrative) (One-time Transaction) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2013 USD ($)	Jun. 30, 2021 INR (₨)	Dec. 31, 2020 USD ($)	Apr. 30, 2018 INR (₨)
One-time Transaction [Table] [Line Items]
Income tax expense	$ 184	$ 134	$ 344	$ 276
Long-term investments [Member]
One-time Transaction [Table] [Line Items]
Restricted investments	397		397					$ 405
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member]
One-time Transaction [Table] [Line Items]
Deposits assets	$ 67		$ 67					68	₨ 5,000,000,000
Desposits assets, percent disputed tax amount	15.00%		15.00%				15.00%
Restricted investments initially deposited	$ 377		$ 377					384	₨ 28,000,000,000
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | Other Noncurrent Assets [Member]
One-time Transaction [Table] [Line Items]
Deposits assets	67		67					$ 68
Indian Income Tax Department (ITD) [Member] | Foreign tax authority [Member] | 2016 India Cash Remittance [Member]
One-time Transaction [Table] [Line Items]
Income tax expense					$ 135
Foreign earnings repatriated					$ 2,800
Income tax, disputed amount	$ 444		$ 444				₨ 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