Long-Term Debt - Debt Instrument Redemption (Details) - Subsequent Event $ in Millions	Jul. 31, 2020 USD ($)
Long-term Debt
Principal Amount Accepted	$ 1,997
Variable rate bonds due February 2021
Long-term Debt
Principal Amount Accepted	$ 473
Senior Notes | 4.1% senior notes due February 2021
Long-term Debt
Interest rate	4.10%
Principal Amount Accepted	$ 943
Senior Notes | 4.85% senior notes due March 2021
Long-term Debt
Interest rate	4.85%
Principal Amount Accepted	$ 530
Senior Notes | 2.6% senior notes due August 2021
Long-term Debt
Interest rate	2.60%
Principal Amount Accepted	$ 51