Long-term Debt and Other Borrowings - Key Information Of Senior Notes (Details) - USD ($)	Dec. 31, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Face Value	$ 3,550,000,000	$ 3,550,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Face Value	3,550,000,000	3,550,000,000
Senior Notes [Member] | Variable-rate Notes due 2021 [Member]
Debt Instrument [Line Items]
Face Value	600,000,000	600,000,000
Senior Notes [Member] | 2022 Notes [Member]
Debt Instrument [Line Items]
Face Value	$ 750,000,000	$ 750,000,000
Interest rate, stated percentage	2.95%	2.95%
Senior Notes [Member] | 2024 Notes [Member]
Debt Instrument [Line Items]
Face Value	$ 400,000,000	$ 400,000,000
Interest rate, stated percentage	3.75%	3.75%
Senior Notes [Member] | 2025 Notes [Member]
Debt Instrument [Line Items]
Face Value	$ 500,000,000	$ 500,000,000
Interest rate, stated percentage	3.625%	3.625%
Senior Notes [Member] | 2027 Notes [Member]
Debt Instrument [Line Items]
Face Value	$ 800,000,000	$ 800,000,000
Interest rate, stated percentage	3.30%	3.30%
Senior Notes [Member] | 2029 Notes [Member]
Debt Instrument [Line Items]
Face Value	$ 500,000,000	$ 500,000,000
Interest rate, stated percentage	2.75%	2.75%