Debt (Details) - Credit Agreement - Revolving Credit Agreement [Member] - USD ($)			9 Months Ended
	Jun. 04, 2018	Jun. 03, 2018	Sep. 30, 2018
Revolving Credit Agreement Entered Into on June 4, 2018 [Member]
Line of Credit Facility
Credit agreement, term (in years)	5 years
Credit agreement, maximum borrowing capacity	$ 1,000,000,000.0
Credit agreement, covenant terms			Pursuant to the credit agreement covenants, the Company must maintain a minimum consolidated net worth, defined as shareholders’ equity determined in accordance with GAAP (excluding accumulated other comprehensive income (loss)) plus (a) trust preferred securities (not to exceed 15% of total capital) and (b) mandatorily convertible securities (combined with trust preferred securities, not to exceed 25% of total capital), less goodwill and other intangible assets. That threshold is adjusted downward by an amount equal to 70% of the aggregate amount of common stock repurchased by the Company after March 31, 2018, up to a maximum deduction of $1.75 billion.  The threshold was $13.719 billion at September 30, 2018 and could decline to a minimum of $12.494 billion during the term of the credit agreement, subject to the Company repurchasing an additional $1.75 billion of its common stock. In addition, the credit agreement contains other customary restrictive covenants as well as certain customary events of default, including with respect to a change in control, which would occur upon the acquisition of 35% or more of the Company’s voting stock or certain changes in the composition of the Company’s Board of Directors.
Maximum percentage of trust preferred securities relative to total capital in determining consolidated net worth			15.00%
Maximum percentage of trust preferred securities and mandatorily convertible securities relative to total capital in determining consolidated net worth			25.00%
Percentage of aggregate amount of common stock repurchased by the Company after March 31, 2018 by which the threshold is adjusted downward			70.00%
Maximum downward adjustment to threshold relative to common stock repurchases			$ 1,750,000,000.00
Credit agreement, threshold of consolidated net worth			13,719,000,000
Common stock repurchases required during the term of the credit agreement to reduce threshold net worth to minimum amount reported			$ 1,750,000,000
Percentage of Company's voting stock acquired by outside entity that would be considered a change in control			35.00%
Credit agreement, compliance			At September 30, 2018, the Company was in compliance with these covenants.
Revolving Credit Agreement Entered Into on June 4, 2018 [Member] | Minimum [Member]
Line of Credit Facility
Credit agreement, threshold of consolidated net worth			$ 12,494,000,000
Revolving Credit Agreement Entered Into on June 4, 2018 [Member] | LIBOR [Member]
Line of Credit Facility
Credit agreement, cost of borrowing, basis points above LIBOR			1.00%
Revolving Credit Agreement Entered Into on June 4, 2018 [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility
Credit agreement, cost of borrowing, basis points above LIBOR			0.75%
Revolving Credit Agreement Entered Into on June 4, 2018 [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility
Credit agreement, cost of borrowing, basis points above LIBOR			1.375%
Revolving Credit Agreement Due to Expire on June 7, 2018 [Member]
Line of Credit Facility
Credit agreement, term (in years)		5 years
Credit agreement, maximum borrowing capacity		$ 1,000,000,000.0