Accounting and Disclosure Changes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash receipts from operating cash flows	$ 1,009	$ 505
Cash receipts from investing cash flows	(971)	(672)
Accounting Standards Update 2018-2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of tax effects from accumulated other comprehensive income to retained earnings	$ 58
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash receipts from operating cash flows		(147)
Cash receipts from investing cash flows		$ 147