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 $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Fair Value Of Plan Investments	$ 1,514	$ 1,471
Private Placement [Member]
Defined Benefit Plan Fair Value Of Plan Investments	26	28
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Fair Value Of Plan Investments	801	773
Fair Value, Inputs, Level 1 [Member] | Private Placement [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Fair Value Of Plan Investments	687	670
Fair Value, Inputs, Level 2 [Member] | Private Placement [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Fair Value Of Plan Investments	26	28
Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plan Fair Value Of Plan Investments	26	28
Equity Securities [Member] | Common Stock [Member]
Defined Benefit Plan Fair Value Of Plan Investments	368	371
Equity Securities [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	494	538
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Fair Value Of Plan Investments	368	370
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	154	181
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Common Stock [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	1
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	340	357
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | US Treasury and Government [Member]
Defined Benefit Plan Fair Value Of Plan Investments	236	198
Fixed Income Securities [Member] | Corporate and municipal bonds and notes [Member]
Defined Benefit Plan Fair Value Of Plan Investments	344	311
Fixed Income Securities [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	43	24
Fixed Income Securities [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Fair Value Of Plan Investments	2
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Fair Value Of Plan Investments	236	198
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate and municipal bonds and notes [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	43	24
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate and municipal bonds and notes [Member]
Defined Benefit Plan Fair Value Of Plan Investments	344	311
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Fair Value Of Plan Investments	2
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate and municipal bonds and notes [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Collective Investments And Mutual Funds [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed Securities [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0
Derivative [Member] | Other Assets [Member]
Defined Benefit Plan Fair Value Of Plan Investments	1	1
Derivative [Member] | Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]
Defined Benefit Plan Fair Value Of Plan Investments	0	0
Derivative [Member] | Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]
Defined Benefit Plan Fair Value Of Plan Investments	1	1
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Defined Benefit Plan Fair Value Of Plan Investments	$ 0	$ 0