Debt (Tender Offers) (Details) - Senior Notes [Member] $ in Millions	Jun. 30, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 4,042
2.850%, Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 795
Debt instrument, interest rate, stated percentage	2.85%
2.950%, Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 132
Debt instrument, interest rate, stated percentage	2.95%
4.000%, Notes Due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 624
Debt instrument, interest rate, stated percentage	4.00%
3.800%, Notes Due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 655
Debt instrument, interest rate, stated percentage	3.80%
4.400%, Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 430
Debt instrument, interest rate, stated percentage	4.40%
4.800%, Notes Due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 1,094
Debt instrument, interest rate, stated percentage	4.80%
9.950%, Notes Due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 65
Debt instrument, interest rate, stated percentage	9.95%
10.200%, Notes Due 2039 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 18
Debt instrument, interest rate, stated percentage	10.20%
6.200%, Notes Due 2059 [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount	$ 229
Debt instrument, interest rate, stated percentage	6.20%