Supplemental Cash Flow Information - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfer from Investments	$ 128	$ 18
Non-cash financing activities related to the issuance of shares for vested restricted stock units	46	$ 27
Operating lease, payments	37
ROU asset obtained in exchange for operating lease liability	502
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ROU asset obtained in exchange for operating lease liability	$ 488