Common and Preferred Shares (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Common shares, authorized (in shares)	3,600,000,000	3,600,000,000	3,600,000,000
Authorized shares and a reconciliation of common shares issued and outstanding
Shares issued and outstanding at beginning of year (in shares)	847,000,000	859,000,000	904,000,000
Common shares repurchased (in shares)	(40,000,000)	(15,000,000)	(50,000,000)
Other, primarily stock option exercises and RSAs granted (in shares)	3,000,000	3,000,000	5,000,000
Shares issued and outstanding as of December 31 (in shares)	810,000,000	847,000,000	859,000,000
Stockholders' Equity Note (Textuals) [Abstract]
Shares reserved for issuance under employee stock and employee benefit plans	19,000,000