Supplemental Cash Flow Information - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfer from Investments	$ 179	$ 41
Non-cash financing activities related to the issuance of shares for vested restricted stock units	48	$ 30
Operating lease, payments	76
ROU asset obtained in exchange for operating lease liability	521
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