Accounting Principles and Practices (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment amount to decrease retained earnings	$ (3,695)	$ (3,260)		$ (3,449)	$ (3,913)	$ (4,862)	$ (4,219)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment amount to decrease retained earnings	$ (1,751)	$ (1,455)		(1,254)	$ (1,669)	$ (2,555)	$ (2,093)
Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment amount to decrease retained earnings				6
Cumulative Effect, Period Of Adoption, Adjustment | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment amount to decrease retained earnings			$ 6	$ 6