Supplementary Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash paid during the year:
Interest	$ 34	$ 102	$ 125
Income taxes	204	528	367
Investing activities:
Change in proceeds of sales of investments available for sale receivable in period	(3)	3	7
Change in purchases of investments available for sale payable in period	(2)	(9)	19
Financing activities:
Fair value of assets acquired	50	595	625
Less: Total purchase price	33	481	557
Liabilities and noncontrolling interests assumed	17	114	68
Change in treasury stock purchases payable in period	1	0	8
Change in accrued dividends payable in period	$ 2	$ (1)	$ 1