Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance			$ (11)
Accumulated other comprehensive income (loss), start of period	$ (1,016)	$ (1,827)	(1,203)	$ (1,192)	$ (2,039)
Other comprehensive income (loss) before reclassifications	175	171
Amounts reclassified from accumulated other comprehensive (income) loss	12	41
Other comprehensive income (loss)	187	212
Accumulated other comprehensive income (loss), end of period	(1,016)	(1,827)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance			0
Accumulated other comprehensive income (loss), start of period	(1,021)	(1,823)	(1,205)	(1,205)	(1,970)
Other comprehensive income (loss) before reclassifications	183	145
Amounts reclassified from accumulated other comprehensive (income) loss	1	2
Other comprehensive income (loss)	184	147
Accumulated other comprehensive income (loss), end of period	(1,021)	(1,823)
Pension and other postretirement benefits
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance			0
Accumulated other comprehensive income (loss), start of period	37	18	46	46	14
Other comprehensive income (loss) before reclassifications	(2)	8
Amounts reclassified from accumulated other comprehensive (income) loss	(7)	(4)
Other comprehensive income (loss)	(9)	4
Accumulated other comprehensive income (loss), end of period	37	18
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance			0
Accumulated other comprehensive income (loss), start of period	(18)	(65)	(41)	(41)	(115)
Other comprehensive income (loss) before reclassifications	5	10
Amounts reclassified from accumulated other comprehensive (income) loss	18	40
Other comprehensive income (loss)	23	50
Accumulated other comprehensive income (loss), end of period	(18)	(65)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Adjustment to adopt recognition and measurement of financial assets and liabilities guidance			(11)
Accumulated other comprehensive income (loss), start of period	(14)	43	$ (3)	$ 8	$ 32
Other comprehensive income (loss) before reclassifications	(11)	8
Amounts reclassified from accumulated other comprehensive (income) loss	0	3
Other comprehensive income (loss)	(11)	11
Accumulated other comprehensive income (loss), end of period	$ (14)	$ 43