Consolidated Balance Sheet and Mini Balance Sheet (Paranthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	1,100,000,000	1,100,000,000
Common Stock, Shares, Issued	491,993,371	489,883,553
Common Stock, Shares, Outstanding		437,053,936
Treasury Stock, Shares	59,302,489	52,829,617
Held-to-maturity Securities, Fair Value	$ 1,895	$ 1,865
End of Period [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common Stock, Shares, Outstanding	432,690,882	437,054,000