Total Equity (Cumulative Adjustments to Retained Earnings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cumulative adjustment for accounting changes	$ (131)	$ 10
Retained Earnings
Cumulative adjustment for accounting changes	306	(35)
Retained Earnings | Revenue from Contracts with Customers
Cumulative adjustment for accounting changes	(32)
Retained Earnings | Derivatives and Hedging-Targeted Improvements to Accounting for Hedging Activities
Cumulative adjustment for accounting changes	(99)
Retained Earnings | Reclassification of Certain Tax Effects from AOCI
Cumulative adjustment for accounting changes	443
Retained Earnings | Improvements to Employee Share-Based Payment Accounting
Cumulative adjustment for accounting changes		(30)
Retained Earnings | Intra-Entity Transfers of Assets Other Than Inventory
Cumulative adjustment for accounting changes		$ (5)
Retained Earnings | Other
Cumulative adjustment for accounting changes	$ (6)