Employee Benefit Plans (Fair Values of the Corporation's Qualified Defined Benefit Pension Plan Investments Measured at Fair Value on a Recurring Basis) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Fair value of plan assets in qualified defined benefit pension plan	$ 2,531,000,000	$ 2,028,000,000
Cash equivalent securities, mutual funds
Fair value of plan assets in qualified defined benefit pension plan	390,000,000	23,000,000
Equity securities | Collective investments funds
Fair value of plan assets in qualified defined benefit pension plan	466,000,000	463,000,000
Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	76,000,000	73,000,000
Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	499,000,000	483,000,000
Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	359,000,000	329,000,000
Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	659,000,000	496,000,000
Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	9,000,000	4,000,000
Debt securities | U.S. government agency mortgage-backed securities
Fair value of plan assets in qualified defined benefit pension plan		2,000,000
Debt securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan		113,000,000
Private placements
Fair value of plan assets in qualified defined benefit pension plan	73,000,000	36,000,000
Securities purchased under agreements to resell
Fair value of plan assets in qualified defined benefit pension plan		6,000,000
Level 1
Fair value of plan assets in qualified defined benefit pension plan	1,324,000,000	1,021,000,000
Level 1 | Cash equivalent securities, mutual funds
Fair value of plan assets in qualified defined benefit pension plan	390,000,000	23,000,000
Level 1 | Equity securities | Collective investments funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 1 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	76,000,000	73,000,000
Level 1 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	499,000,000	483,000,000
Level 1 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	359,000,000	329,000,000
Level 1 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 1 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 1 | Debt securities | U.S. government agency mortgage-backed securities
Fair value of plan assets in qualified defined benefit pension plan		0
Level 1 | Debt securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan		113,000,000
Level 1 | Private placements
Fair value of plan assets in qualified defined benefit pension plan
Level 1 | Securities purchased under agreements to resell
Fair value of plan assets in qualified defined benefit pension plan		0
Level 2
Fair value of plan assets in qualified defined benefit pension plan	1,134,000,000	971,000,000
Level 2 | Cash equivalent securities, mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Equity securities | Collective investments funds
Fair value of plan assets in qualified defined benefit pension plan	466,000,000	463,000,000
Level 2 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	659,000,000	496,000,000
Level 2 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	9,000,000	4,000,000
Level 2 | Debt securities | U.S. government agency mortgage-backed securities
Fair value of plan assets in qualified defined benefit pension plan		2,000,000
Level 2 | Debt securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan		0
Level 2 | Private placements
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 2 | Securities purchased under agreements to resell
Fair value of plan assets in qualified defined benefit pension plan		6,000,000
Level 3
Fair value of plan assets in qualified defined benefit pension plan	73,000,000	36,000,000
Level 3 | Cash equivalent securities, mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Equity securities | Collective investments funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Equity securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Equity securities | Common stock
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | U.S. Treasury and other U.S. government agency securities
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | Corporate and municipal bonds and notes
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | Collateralized mortgage obligations
Fair value of plan assets in qualified defined benefit pension plan	0	0
Level 3 | Debt securities | U.S. government agency mortgage-backed securities
Fair value of plan assets in qualified defined benefit pension plan		0
Level 3 | Debt securities | Mutual funds
Fair value of plan assets in qualified defined benefit pension plan		0
Level 3 | Private placements
Fair value of plan assets in qualified defined benefit pension plan	73,000,000	36,000,000
Level 3 | Securities purchased under agreements to resell
Fair value of plan assets in qualified defined benefit pension plan		$ 0