Consolidated Balance Sheet and Mini Balance Sheet (Paranthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
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	489,883,553	485,707,644
Common Stock, Shares, Outstanding	437,053,936	467,000,306
Treasury Stock, Shares	52,829,617	18,707,338
Held-to-maturity Securities, Fair Value	$ 1,865	$ 789