Segment and Related Information (Geographic Data) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 11,499	$ 11,721	$ 12,132
Long-lived assets	35,514	34,022
US [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	8,878	9,318	9,796
Long-lived assets	23,572	22,638
UK [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	2,621	2,403	2,336
Long-lived assets	$ 11,942	$ 11,384