Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions		3 Months Ended	12 Months Ended
Oct. 15, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income		$ 215	$ 187
Less: preferred stock dividends declared		(1)	(1)
Net income available to the Company's common shareholders - basic		214	186
Add: Interest expense related to convertible notes		0	4
Net income available to the Company's common shareholders - diluted		$ 214	$ 190
Average shares outstanding - basic (in shares)		435	471
Effect of dilutive securities:
Stock options (in shares)		1	0
Stock and performance awards (in shares)		4	4
Convertible notes (in shares)		0	14
Average shares outstanding - diluted (in shares)		440	489
Common stock outstanding (in shares)		436	453
Incremental common shares attributable to dilutive effect of accelerated share repurchase agreements (in shares)				55
Convertible notes
Effect of dilutive securities:
Number of shares of common stock previously attributable to the convertible notes (in shares)	15

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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