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Other Financial Data - Earnings Per Common Share (Details) $ / shares in Units, shares in Millions		3 Months Ended								12 Months Ended
	Sep. 05, 2019 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares	Sep. 28, 2019 USD ($) $ / shares	Jun. 29, 2019 USD ($) $ / shares	Mar. 30, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 29, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Aug. 25, 2015
Basic earnings per common share:
Earnings (loss) \| $		$ 244,000,000	$ 267,000,000	$ 207,000,000	$ 151,000,000	$ 423,000,000	$ 247,000,000	$ 180,000,000	$ 117,000,000	$ 868,000,000	$ 966,000,000	$ (155,000,000)
Weighted average common shares outstanding (in shares)										166.6	162.4	162.9
Per share amount (US$ per share) \| $ / shares		$ 1.43	$ 1.60	$ 1.25	$ 0.92	$ 2.58	$ 1.52	$ 1.11	$ 0.73	$ 5.21	$ 5.95	$ (0.95)
Diluted earnings per common share:
Earnings (loss) \| $		$ 244,000,000	$ 267,000,000	$ 207,000,000	$ 151,000,000	$ 423,000,000	$ 247,000,000	$ 180,000,000	$ 117,000,000	$ 868,000,000	$ 966,000,000	$ (155,000,000)
Weighted average common shares outstanding (in shares)										166.6	162.4	162.9
Add effect of dilutive securities:
Share-based awards (in shares)										4.7	4.2	0.0
Diluted weighted average common shares outstanding (in shares)										175.6	172.0	162.9
Per share amount (US$ per share) \| $ / shares		$ 1.39	$ 1.51	$ 1.18	$ 0.86	$ 2.44	$ 1.43	$ 1.05	$ 0.69	$ 4.95	$ 5.62	$ (0.95)
2.0% senior convertible notes due 2020
Add effect of dilutive securities:
Senior Convertible Notes (in shares)										4.3	5.4	0.0
1.75% senior convertible notes due 2024
Add effect of dilutive securities:
Senior Convertible Notes (in shares)										0.0	0.0	0.0
Convertible Debt \| 2.0% senior convertible notes due 2020
Add effect of dilutive securities:
Debt instrument face principal amount \| $	$ 800,000,000												$ 1,000,000,000.0
Debt instrument stated interest rate													2.00%	2.00%
Convertible debt conversion ratio			0.0149186
Convertible debt conversion price (US$ per share) \| $ / shares			$ 67.03
Convertible Debt \| 1.75% senior convertible notes due 2024
Add effect of dilutive securities:
Debt instrument face principal amount \| $	$ 1,000,000,000.0
Debt instrument stated interest rate	1.75%
Convertible debt conversion ratio	0.0049140
Convertible debt conversion price (US$ per share) \| $ / shares	$ 203.50
Stock Options
Add effect of dilutive securities:
Stock options excluded from computation of dilutive shares due to antidilutive nature (in shares)										0.3	0.8	8.7
Performance Options
Add effect of dilutive securities:
Stock options excluded from computation of dilutive shares due to antidilutive nature (in shares)										0.1	0.6
RSU's
Add effect of dilutive securities:
Stock options excluded from computation of dilutive shares due to antidilutive nature (in shares)												1.4
Convertible Debt Securities
Add effect of dilutive securities:
Stock options excluded from computation of dilutive shares due to antidilutive nature (in shares)												3.1