Shareholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	19,110	[1]	53,768	[2]
Dollar Value of Shares Repurchased	$ 1,327	[1]	$ 4,421	[2]
Remaining Dollar Value of Shares that may be Repurchased	588
Value of share repurchases with trade dates prior to current reporting date but with settlement dates subsequent to the current reporting date.	$ 24		$ 105
Number of shares repurchased with trade dates prior to current reporting date but with settlement dates subsequent to the current reporting date.	300		1,200
Value of shares repurchased with trade dates prior to the current reporting quarter, but settlement dates in the current quarter	$ 45
Number of shares repurchased with trade dates prior to the current reporting quarter, but settlement dates in the current quarter	700
December 2015 [Member]
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	0		13,369
Dollar Value of Shares Repurchased	$ 0		$ 933
Remaining Dollar Value of Shares that may be Repurchased	$ 0
March 2016 [Member]
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	0		2,823
Dollar Value of Shares Repurchased	$ 0		$ 228
Remaining Dollar Value of Shares that may be Repurchased	$ 0
May 2016 [Member]
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	0		37,576
Dollar Value of Shares Repurchased	$ 0		$ 3,260
Remaining Dollar Value of Shares that may be Repurchased	$ 0
November 2016 [Member]
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	19,110		0
Dollar Value of Shares Repurchased	$ 1,327		$ 0
Remaining Dollar Value of Shares that may be Repurchased	$ 588

[1] Includes the effect of $24 million in share repurchases (0.3 million shares) with trade dates on, or prior to, September 30, 2017, but cash settlement dates subsequent to September 30, 2017, and excludes the effect of $45 million in share repurchases (0.7 million shares) with trade dates on, or prior to, December 31, 2016, but cash settlement dates subsequent to December 31, 2016.

[2] (b)Includes the effect of $105 million in share repurchases (1.2 million shares) with trade dates on, or prior to, September 30, 2016, but cash settlement dates subsequent to September 30, 2016.