Share-based compensation (Pre-tax and After-tax Share-based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax	$ 153	$ 109	$ 108
Share-based compensation expense, after-tax	89	64	70
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax	24	22	23
Share-based compensation expense, after-tax	18	17	17
Additional Paid-in Capital
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	$ 36	$ 18	$ 6