Outstanding and Weighted Average Common Shares - Changes in Corporation's Outstanding Common Shares (Detail)	5 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Balance at January 1		325,314,177	341.5	340.0
Activity related to restricted common stock awards, net		600,000	800,000	1,300,000
Stock options exercised		3,300,000	2,300,000	200,000
Shares repurchased	(19,300,000)	(43,400,000)	(19,300,000)
Balance at December 31	325,314,177	285,834,964	325,314,177	341.5