CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Common shares [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Treasury shares [Member]	AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting policy | Cumulative effect of adoption of equity securities guidance	$ 0			$ 1		$ (1)
Beginning balance (in shares) at Dec. 31, 2017		146,634,664
Beginning balance at Dec. 31, 2017	5,995	$ 3	$ 8,085	11,326	$ (13,648)	229
Comprehensive income (loss) [Abstract]
Net income	594			594
Total other comprehensive income (loss), net of tax	(233)					(233)
Total comprehensive income	361
Dividends to shareholders	(125)			(125)
Repurchase of common shares (in shares)		(3,003,729)
Repurchase of common shares	(482)				(482)
Share-based compensation plans (in shares)		1,387,422
Share-based compensation plans	91		31		60
Ending balance (in shares) at Mar. 31, 2018		145,018,357
Ending balance at Mar. 31, 2018	5,840	$ 3	8,116	11,796	(14,070)	(5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting policy	1
Cumulative effect of change in accounting policy | Cumulative effect of adoption of premium amort on purchased callable debt	(5)			(5)
Beginning balance (in shares) at Dec. 31, 2018		136,330,747
Beginning balance at Dec. 31, 2018	5,588	$ 3	8,260	12,909	(15,293)	(291)
Comprehensive income (loss) [Abstract]
Net income	395			395
Total other comprehensive income (loss), net of tax	326					326
Total comprehensive income	721
Dividends to shareholders	(127)			(127)
Repurchase of common shares (in shares)		(3,199,907)
Repurchase of common shares	(399)				(399)
Share-based compensation plans (in shares)		1,052,667
Share-based compensation plans	65		10		55
Ending balance (in shares) at Mar. 31, 2019		134,183,507
Ending balance at Mar. 31, 2019	$ 5,843	$ 3	$ 8,270	$ 13,172	$ (15,637)	$ 35