Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value
Financial assets (liabilities)
Cash and equivalents	$ 7	$ 20
Available-for-sale debt securities	123
Available-for-sale debt securities		117
Equity securities	55	54
Other investments	4
Other investments		4
Cash flow hedges	(63)	(105)
Short- and long-term debt principal	(12,956)	(3,974)
Carrying Value
Financial assets (liabilities)
Cash and equivalents	7	20
Available-for-sale debt securities	123
Available-for-sale debt securities		117
Equity securities	55	54
Other investments	4
Other investments		4
Cash flow hedges	(63)	(105)
Short- and long-term debt principal	(13,191)	(4,032)
Fair Value, Inputs, Level 1
Financial assets (liabilities)
Cash and equivalents	2	15
Available-for-sale debt securities	0
Available-for-sale debt securities		0
Equity securities	55	54
Other investments	0
Other investments		0
Cash flow hedges	0	0
Short- and long-term debt principal	0	0
Fair Value, Inputs, Level 2
Financial assets (liabilities)
Cash and equivalents	5	5
Available-for-sale debt securities	123
Available-for-sale debt securities		117
Equity securities	0	0
Other investments	0
Other investments		0
Cash flow hedges	(63)	(105)
Short- and long-term debt principal	(12,956)	(3,974)
Fair Value, Inputs, Level 3
Financial assets (liabilities)
Cash and equivalents	0	0
Available-for-sale debt securities	0
Available-for-sale debt securities		0
Equity securities	0	0
Other investments	4
Other investments		4
Cash flow hedges	0	0
Short- and long-term debt principal	$ 0	$ 0